Vibrator, vibratory gyroscope, and vibration adjusting method

ABSTRACT

A vibrator for a vibratory gyroscope including a base part and at least one bending-vibration piece extending from the base part in a direction crossing the longitudinal direction of the base part and a fixing part for fixing one end of the base part. The base part and bending-vibration piece are formed to extend substantially in a specified plane. At the opposite side to one end of the base part, a projection projecting from the bending-vibration piece is provided, or at least a pair of resonant arms resonating with vibration of the base part, wherein the resonant arms project from the fixing part. With this arrangement, it is possible to detect a turning angular rate with high accuracy.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a Continuation-in-Part Application of U.S. Ser. No.09/884,288, filed Jun. 19, 2001, now allowed, which is a ContinuationApplication of U.S. Ser. No. 09/420,350, filed Oct. 19, 1999, now U.S.Pat. No. 6,346,765, which is a Continuation Application of U.S. Ser. No.08/991,011, filed Dec. 15, 1997, now U.S. Pat. No. 6,018,212, which is aContinuation-in-Part of U.S. Ser. No. 08/971,686, filed Nov. 17, 1997,now U.S. Pat. No. 5,998,911. The entireties of the above applicationsare incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a vibrator used for an angularrate sensor used for detecting a turning angular rate in a turningsystem and a vibratory gyroscope using the same vibrator, andparticularly to a vibrator using a piezoelectric member and a vibratorygyroscope using the same vibrator.

[0004] 2. Description of the Related Art

[0005] Up to now, as an angular rate sensor used for detecting a turningangular rate in a turning system, a vibratory gyroscope using apiezoelectric member has been used for detecting position of anaircraft, a ship, a space satellite, or the like. Recently, it is usedin a car-navigation system, a movement detecting mechanism of a VTR or astill camera, and the like in the field of public livelihood.

[0006] Such a vibratory gyroscope utilizes the phenomenon that when anangular speed is applied to a vibrating object, a Coriolis force isgenerated in the direction perpendicular to the vibratory direction. Itsmechanism is analyzed by using a dynamic model (for example, “Handbookof Elastic Wave Device Technologies” (Danseiha-Sosi Gijutsu Handbook)issued by Ohm, Inc., pp.491 to 497). Various kinds of piezoelectricvibratory gyroscopes have been proposed up to now. For example, a Sperrytuning-fork gyroscope, a Watson tuning-fork gyroscope, aregular-triangle prism-shaped tuning-piece gyroscope, a cylindricaltuning-piece gyroscope, and the like are known as a piezoelectricvibratory gyroscope.

[0007] The inventors are studying various applications of vibratorygyroscopes, and have studied using a vibratory gyroscope as a turningrate sensor used in a car control method of an automobile body turningrate feedback system, for example. Such a system detects the directionof a steering wheel itself by a turning angle of the steering wheel. Atthe same time as this, the system detects the actual turning rate of thecar body by means of a vibratory gyroscope. The system finds adifference between the direction of the steering wheel and the actualbody turning rate by comparing them with each other, and attains astable body control by compensating a wheel torque and a steering angleon the basis of this difference.

[0008] However, any example of the above-mentioned former piezoelectricvibratory gyroscopes can detect a turning angular rate only by arranginga vibrator in parallel with the axis of turning (what is called avertical arrangement). The turning axis of a turning system to bemeasured is usually perpendicular to the gyroscope mounting part.Accordingly, in mounting such a piezoelectric vibratory gyroscope it hasbeen impossible to shorten the piezoelectric vibratory gyroscope inheight, namely, to reduce the piezoelectric vibratory gyroscope in sizein the direction of the turning axis.

[0009] In recent years, a piezoelectric vibratory gyroscope capable ofdetecting a turning angular rate even when arranging a vibratorperpendicularly to the turning axis (what is called a horizontalarrangement) has been proposed in a Japanese laid-open publicationTokkaihei No.8-128833. In this example, as shown as an example in FIG.1, a vibrator extends in the directions X and Y, namely, extendsperpendicularly to the turning axis Z. Each of three elastic members 51a, 51 b and 51 c is provided with a weight 53 at one end thereof. Theelastic members 51 a, 51 b and 51 c are vibrated by piezoelectricdevices 54 and 55 in the X-Y plane in phase inverse to one another. ACoriolis force in the Y direction generated by a turning angular rate ωaround the Z axis is applied to the center of gravity of the weight 53.Since the plane of the elastic members 51 a, 51 b and 51 c and thecenter of gravity of the weight 53 are slightly distant in the Zdirection from each other, the ends of the elastic members 51 a, 51 band 51 c are bent reversely to one another in the Z direction by theCoriolis forces each of which is applied to the center of gravity of theweight 53. A turning angular rate ω around the Z axis is obtained bydetecting this bending vibration by means of piezoelectric devices 56and 57.

[0010] And up to now, various configurations have been known as avibratory gyroscope using a vibrator which is composed of plural armsand a base part joining the plural arms, gives a drive vibration in aspecified plane to each of the arms, and obtains a turning angular rateon the basis of a detection vibration which is perpendicular to thisdrive vibration and corresponds to the applied turning angular rate. Forexample, a Japanese laid-open publication Tokkaihei No. 7-83671 hasdisclosed a vibratory gyroscope using a tuning-fork vibrator made byjoining three arms composed of a middle drive arm and two detection armsat both sides of the middle drive arm in one body at the base part. FIG.2 shows a configuration of such a former vibratory gyroscope. In theexample shown in FIG. 2, a vibrator 102 forming a vibratory gyroscope iscomposed of three arms which are composed of a middle drive arm 104 andtwo detection arms 103 and 105 arranged at both sides of it nearly inparallel with it, and a base 106 at which the drive arm 104 and thedetection arms 103 and 105 are joined in one body with one another.

[0011] In the above-mentioned tuning-fork vibrator 102, the drive arm104 is vibrated in the X-Z plane by an unillustrated driving meansprovided on the drive arm. And the left and right detection arms 103 and105 are resonated in the same X-Z plane. When a turning angular rate ωacts around the axis Z of symmetry of the tuning-fork vibrator 102, aCoriolis force f acts on each of the detection arms 103 and 105. Sincethe detection arms 103 and 105 are vibrating in the X-Z plane, vibrationin the Y-Z plane is induced in the detection arms 103 and 105. A turningangular rate is measured by detecting this vibration by means of anunillustrated detecting means provided on each of the detection arms 103and 105.

[0012] A piezoelectric vibratory gyroscope disclosed in theabove-mentioned Japanese laid-open publication Tokkaihei No. 8-128833can certainly detect a turning angular rate using the Coriolis principleeven when the vibrator is arranged horizontally. However, necessity ofproviding the weight 53 makes it insufficient to shorten the gyroscopein height. And when the weight 53 is made thin in thickness in order tosufficiently shorten it in height, moment by a Coriolis force is madesmall and a bending vibration is made very small, and there is a problemthat a measurement sensitivity is lowered.

[0013] And in a vibrator of a piezoelectric vibratory gyroscope havingthe above-mentioned configuration, the drive vibration and the detectionvibration are different in the vibrating direction from each other dueto configuration of the vibrator. That is to say, that vibrator needssuch vibrations in two directions that the elastic members 51 a, 51 band 51 c which are vibrating in the X-Y plane need to vibrate also inthe Z direction. Generally in a piezoelectric vibratory gyroscope, it isrequired to keep always a constant relation between a vibrationfrequency for driving and a vibration frequency for detection in orderto keep a good measurement sensitivity. Now, considering a singlecrystal as a material for a vibrator, since a single crystal isanisotropic, variation in vibration frequency caused by a temperaturechange varies with the direction of vibration. Therefore, attempting toform a vibrator having the above-mentioned configuration out of a singlecrystal causes a problem that even in case of setting a constantrelation between a drive vibration frequency and a detecting vibrationfrequency at a certain temperature, when the temperature is changed therelation cannot be kept and the measurement sensitivity is liable tovary with temperature.

[0014] In a former vibratory gyroscope of the above-mentionedcomposition shown in FIG. 2, in case of forming the vibratory gyroscopeby supporting the tuning-fork vibrator 102, the vibrator 102 issupported by fixing the entire end part 107 of the base part 106 of thetuning-fork vibrator 102 opposite to the end part at which the drive arm104 and the detection arms 103 and 105 exist, or by fixing anunillustrated supporting arm at a position of this end part 107corresponding to the axis Z of symmetry. Therefore, it cannot be saidthat a Coriolis force generated by a turning angular rate is efficientlyutilized for action of detection vibration in the detection arms 103 and105, and there is a problem that sharpness of resonance (Q value) of thedetection vibration in the Y-Z plane in the detection arms 103 and 105is low and the measurement sensitivity is low.

[0015] On the other hand, as a turning angular rate detecting method,both of an ordinary vibratory gyroscope having a vertically-arrangedvibrator and a vibratory gyroscope having the above-mentionedhorizontally-arranged vibrator electrically take in vibration of thevibrator different in mode from a drive vibration generated by aCoriolis force as displacement of a piezoceramic member, and measures aturning angular rate on the basis of the amplitude of the output signal.However, since a vibratory gyroscope having a horizontally-arrangedvibrator composed of a piezoelectric single crystal has a lowsensitivity to a turning angular rate due to its composition, there is aproblem that it deteriorates a detection accuracy to measure a turningangular rate on the basis of the amplitude of an output signal.

[0016] In order to solve the problem of noises caused by such externalfactors as a voltage fluctuation, a temperature change and the like, atechnique which pays attention to a fact that a phase difference betweenthe phase of a driving signal and the phase of an output signal ischanged by a Coriolis force in a vertically-arranged tuning-piecevibrator, and measures a turning angular rate on the basis of variationof the phase difference has been disclosed in Japanese patentpublication Tokkohei No. 4-14734. However, even by applying theabove-mentioned detection of a turning angular rate on the basis ofvariation in phase difference to a vibratory gyroscope having ahorizontally-arranged vibrator composed of a piezoelectric singlecrystal, a satisfactory result cannot be obtained in measurementsensitivity and in linearity of a phase difference to a turning angularrate.

[0017] A problem the present invention attempts to solve is to make itpossible to detect a turning angular rate in a sufficiently highaccuracy without providing a projection having a certain weight from avibrator toward the axis of turning even in case of setting up thevibrator in a direction in which a vibrating arm of the vibrator extendsperpendicularly to the axis of turning.

[0018] Another problem the invention attempts to solve is to provide avibrator which can be simplified in configuration, be horizontallyarranged in mounting, and be reduced in height, a method for adjustingthe same vibrator, and a vibratory gyroscope using the same vibrator.

SUMMARY OF THE INVENTION

[0019] An object of the invention is to provide a vibratory gyroscopecapable of measuring a turning angular rate with high sensitivity bysolving the above-mentioned problems.

[0020] Another object of the invention is to provide a vibratorygyroscope using a horizontally-arranged vibrator composed of apiezoelectric single crystal, the vibratory gyroscope being improved indetection accuracy of a turning angular rate.

[0021] A vibrator according to a first embodiment of the inventioncomprises a main arm provided with a base part and at least onebending-vibration piece extending from the base part in a directioncrossing the longitudinal direction of the base part, and a fixing partfor fixing one end of the base part, wherein the base part and thebending-vibration piece are formed so that they extend substantially ina specified plane.

[0022] The invention also relates to a vibratory gyroscope for detectinga turning angular rate, the vibratory gyroscope including the abovediscussed vibrator, an exciting means for exciting vibration of thevibrator in a plane, and a detecting means for detecting a bendingvibration of the vibrator generated by a Coriolis force to be applied tothe vibrator when the vibrator turns in the plane and outputting asignal according to the detected bending vibration.

[0023] Since according to the invention a drive vibration and adetection vibration of a vibrator take place in a specified plane andthe invention uses a bending vibration as vibration to be detected, theinvention can detect a turning angular rate with sufficiently highsensitivity without providing a projection of a certain weight from thevibrator toward the axis of turning, even when setting up the vibratorso that a vibrating arm of the vibrator extends perpendicularly to theaxis of turning.

[0024] The first preferred embodiment uses a fixing piece which is fixedat both ends of it as a fixing part, and a main arm is provided at oneside of this fixing piece and a resonator piece is provided at the otherside of the fixing piece. The fixing piece, the main arm and theresonator piece are formed so as to extend substantially in a specifiedplane. That is to say, an exciting means and a bending-vibrationdetecting means can be disposed with a fixing piece fixed at both endsbetween them. Thanks to this, since such bad influences aselectromechanical coupling and the like between the exciting means andthe bending-vibration detecting means can be prevented, the detectionaccuracy is improved.

[0025] In the above-mentioned configuration, since displacement of thevibrator is in a plane, the main arm, the resonator arm, and the fixingpiece can be made of the same single crystal, for example, a singlecrystal of quartz, LiTaO₃, or LiNbO₃. In this case, the measurementsensitivity can be improved. The whole of a vibrator can be made bymaking a single crystal thin plate and processing this single crystalthin plate by means of etching or grinding.

[0026] Although the base part and the bending-vibration piece can bemade of different members from each other, it is particularly preferablethat they are formed in one body. Although a material for the vibratoris not limited in particular, it is preferable to use a single crystalof quartz, LiNbO₃, LiTaO₃, a solid solution of lithium niobate-lithiumtantalate (Li(Nb, Ta)O₃, or the like. By using such a single crystal, itis possible to improve a detection sensitivity and reduce a detectionnoise.

[0027] And since such a single crystal is particularly insensitive to atemperature change, it is suitable for a sensor used in a car wherethermal stability is necessary. This point is further described. As anangular speed sensor using a tuning-fork vibrator, there is, forexample, a piezoelectric vibratory gyroscope disclosed in theabove-mentioned Japanese laid-open publication Tokkaihei No. 8-128833.In such a vibrator, however, the vibrator vibrates in two directions.That is to say, in FIG. 1, the vibrator vibrates in the Z direction aswell as in the X-Y plane. Therefore, particularly in case of forming thevibrator out of such a single crystal as described above, it isnecessary to match the characteristics of the single crystal in the twodirections with each other. In practice, however, a piezoelectric singlecrystal is anisotropic.

[0028] Generally in a piezoelectric vibratory gyroscope, in order tokeep good sensitivity, it is required to keep a constant vibrationfrequency difference between a natural resonance frequency of a drivevibration mode and a natural resonance frequency of a detectionvibration mode. However, a single crystal is anisotropic and a degree ofvariation in vibration frequency caused by a temperature change varieswith the crystal face. For example, although variation in vibrationfrequency caused by a temperature change is very little when a singlecrystal is cut along a specific crystal face, variation in vibrationfrequency is very sensitive to a temperature change when a singlecrystal is cut along another crystal face.

[0029] Thus, when a vibrator vibrates in two directions, at least one ofthe two vibrating faces is a crystal face having a large variation invibration frequency caused by a temperature change.

[0030] On the other hand, as shown in the invention, by making the wholeof a vibrator vibrate in a specified plane and forming the vibrator outof a piezoelectric single crystal it is possible to prevent the vibratorfrom being influenced by anisotropy of a single crystal as describedabove and use only the best crystal face in characteristics of thesingle crystal in the vibrator.

[0031] Concretely, since every vibration of a vibrator takes place in asingle plane, it is possible to manufacture a vibrator using only acrystal face having little variation in vibration frequency caused by atemperature change of a single crystal. Therefore, it is possible toprovide a vibratory gyroscope having a very high thermal stability.

[0032] Among the above-mentioned single crystals, single crystals ofLiNbO₃, LiTaO₃, and a single crystal of a solid solution of lithiumniobate-lithium tantalate have particularly large electromechanicalcoupling coefficients. Comparing a single crystal of LiNbO₃ and a singlecrystal of LiTaO₃ with each other, the single crystal of LiTaO₃ has alarger electromechanical coupling coefficient and a better thermalstability than the single crystal of LiNbO₃.

[0033] A vibrator according to a second embodiment of the invention isthe above-mentioned vibrator in which the main arm comprises a pair ofbending-vibration pieces extending in a direction crossing thelongitudinal direction of the base part and a tuning-fork vibrator piecewhose tines extend respectively from the bending-vibration pieces, andthe base part, the bending-vibration pieces and the tuning-fork vibratorpiece are formed so as to extend substantially in a specified plane. Inthe above-mentioned construction, since displacement of the vibrator isin a plane, the bending vibration piece, the tuning-fork vibrator pieceand the base part can be made of the same single crystal, for example, asingle crystal of quartz, LiTaO₃, LiNbO₃, or Li(Nb, Ta)O₃. This case ispreferable, since the measurement sensitivity can be improved and thevibrator can be made of a single crystal thin plate by means of a waferetching process and the like (in case of quartz) or a single crystalcutting method of grinding and the like (in case of a single crystal ofLiTaO₃, LiNbO₃, or the like).

[0034] A vibrator adjusting method of the invention is a method foradjusting a vibrator having the above-mentioned construction, thevibrator being adjusted to a specified relation between the resonancefrequency of vibration of said bending vibration piece and tuning-forkvibrator piece in said single plane and the resonance frequency ofbending vibration of said base part in said single plane, by projectingboth ends of said tuning-fork vibrator piece outwardly from the positionof said bending vibration piece in said same single plane and reducingthe length of at least one of the projected parts.

[0035] A vibratory gyroscope of this invention is a vibratory gyroscopefor detecting a turning angular rate by means of a vibrator of theabove-mentioned second embodiment, said vibratory gyroscope comprisingan exciting means, provided in said tuning-fork vibrator piece, forexciting vibration of said tuning-fork vibrator piece, and bendingvibration piece in said single plane; and a bending-vibration detectingmeans, provided in the base part, for detecting a bending vibrationtaking place in said base part in said single plane and outputting asignal according to the detected bending vibration.

[0036] And a vibratory gyroscope of this invention is a vibratorygyroscope for detecting a turning angular rate by means of a vibrator ofthe above-mentioned second embodiment, said vibratory gyroscopecomprising an exciting means, provided in said base part, for exciting abending movement of said base part in said single plane; and abending-vibration detecting means, provided in the tuning-fork vibratorpiece, for detecting vibration taking place in said tuning-fork vibratorpiece and bending vibration piece in said single plane and outputting asignal according to the detected vibration.

[0037] A vibrator according to a third embodiment of the invention is avibrator wherein said vibrator comprises a main arm provided with a pairof said bending-vibration pieces extending in a direction crossing thelongitudinal direction of the base part and a tuning-fork vibrator piecewhose tines extend respectively from the bending-vibration pieces andadditionally to this main arm, a fixing piece which is fixed at bothends and at which the base part of the main arm is fixed, and aresonator piece provided on the fixing piece at a position which is atthe opposite side to and corresponds to said base part, and wherein saidmain arm, fixing piece, and resonator piece extend in a specified plane.

[0038] It is possible to make a bending movement, having as a fulcrumthe fixing piece, joined with said base part and said resonator piecetake place in said base part and said resonator piece.

[0039] A vibrator adjusting method of this invention is a method foradjusting a vibrator of the third embodiment, the vibrator beingadjusted to a specified relation between the resonance frequency ofvibration of said tuning-fork vibrator piece and bending vibration piecein said single plane and the resonance frequency of bending vibration ofsaid base part and said resonator piece in said single plane, byreducing length of at least one of the projected parts provided at bothends of the bending vibration pieces.

[0040] A vibratory gyroscope of this invention is a vibratory gyroscopefor detecting a turning angular rate by means of a vibrator of the thirdembodiment, said vibratory gyroscope comprising an exciting means,provided in said tuning-fork vibrator piece, for exciting vibration ofsaid tuning-fork vibrator piece in said single plane; and abending-vibration detecting means, provided in the resonator piece, fordetecting a bending vibration taking place in said resonator piece insaid single plane and outputting a signal according to the detectedbending vibration.

[0041] And a vibratory gyroscope of this invention is a vibratorygyroscope for detecting a turning angular rate by means of a vibrator ofthe third embodiment, said vibratory gyroscope comprising an excitingmeans, provided in said resonator piece, for exciting a bending movementof said resonator piece in said single plane; and a vibration detectingmeans, provided in the tuning-fork vibrator piece, for detectingvibration taking place in said tuning-fork vibrator piece in said singleplane and outputting a signal according to the detected vibration.

[0042] In any case of the above-mentioned vibratory gyroscopes, it ispossible to set an exciting means and a bending-vibration detectingmeans or a vibration detecting means at a position more distant from andabove a vibrator in comparison with a former vibrator having noresonator piece. Accordingly, since such bad influences aselectromechanical coupling and the like between the exciting means andthe bending-vibration detecting means or the vibration detecting meanscan be prevented, the detection accuracy is improved.

[0043] A vibratory gyroscope according to a fourth embodiment of theinvention is a vibratory gyroscope comprising one of said vibrators,

[0044] a driving means for driving a drive vibration,

[0045] a detecting means for detecting a vibrating state in a vibrationmode which is caused by the drive vibration generated by the drivingmeans and is different from the drive vibration, and

[0046] a phase difference detecting means for detecting a phasedifference between a reference signal and an output signal, whenassuming that an electrical signal used for generating a drive vibrationis a reference signal and an electrical signal taken by the detectingmeans from a vibration having a vibration mode which is caused by thedrive vibration and is different from the drive vibration;

[0047] said vibratory gyroscope detecting a turning angular rate on thebasis of variation of the phase difference detected by the phasedifference detecting means.

[0048] The invention has been developed by finding that in a vibratorygyroscope comprising a vibrator composed of a piezoelectric singlecrystal using vibration in a horizontal plane as a drive vibration, itis possible to improve detection of a turning angular rate in accuracyby obtaining a phase difference between a reference signal based on adrive vibration and an output signal based on a detection vibration, anddetecting the turning angular rate on the basis of the obtained phasedifference. That is to say, even in such a vibratory gyroscope as avibratory gyroscope using a horizontally-arranged vibrator, saidvibratory gyroscope being a little in vibration of the vibratorgenerated by a Coriolis force and low in sensitivity, it is possible toimprove a gyroscopic signal to be detected in the signal-to-noise ratioof a signal to a noise caused by such external factors as a voltagefluctuation, a temperature change, and the like by using as a materialfor the vibrator a piezoelectric single crystal itself having a high Qvalue, for example, a single crystal of quartz, LiNbO₃, or LiTaO₃. As aresult, in a range in which the amplitude of a signal called a leakagesignal caused by an unnecessary vibration due to an insufficientprocessing accuracy or the like is 7 times larger than the amplitude ofan original gyroscopic signal, it is possible to detect a turningangular rate in a range where the detection sensitivity is low butlinearity of variation in phase difference to a turning angular rate isgood. Therefore, the detection accuracy can be improved.

[0049] A fifth embodiment of the invention is a vibratory gyroscopehaving said vibrator, wherein the vibrator is a plate-shaped vibratorcomposed of a piezoelectric single crystal and layer-shaped parts ofplural layers each of which is composed of a piezoelectric singlecrystal are provided between one main face and the other main face ofthe vibrator, and the axial directions of polarization of the respectivelayer-shaped parts are different from one another.

[0050] This invention relates to a vibratory gyroscope, wherein saidvibrator is provided with one electrode provided on one main face andthe other electrode which is provided on the other main face and isopposite to the one electrode.

[0051] This invention relates to a method for making said vibratorvibrate in a direction crossing the central face of the vibrator, saidmethod providing one electrode on one main face, providing the otherelectrode opposite to the one electrode on the other main face, andapplying alternating voltages different in polarity from each other,respectively, to the one electrode and the other electrode.

[0052] The invention relates to a method for detecting vibration of saidvibrator, said method providing one electrode on one main face,providing the other electrode opposite to the one electrode on the othermain face, connecting the one electrode and the other electrode with avoltage detecting mechanism, and detecting an alternating voltagegenerated between the one electrode and the other electrode by makingthe vibrator vibrate in a direction crossing the one main face and theother main face.

[0053] According to a vibrator and a vibratory gyroscope of the fifthembodiment, it is possible to make the vibrator perform a bendingvibration in a direction crossing, preferably, perpendicular to a mainface by forming electrodes on a pair of main faces of the vibratoropposite to each other and applying an alternating voltage to theseelectrodes. Furthermore, when a bending vibration is excited, anelectric field is uniformly applied to the inside of the vibrator.Therefore, a locally ununiform electric field and an internal stresscaused by the ununiform electric field are not generated inside thevibrator.

[0054] In a preferred embodiment of the invention, the respectivelayer-shaped parts are composed of plate-shaped members each of which iscomposed of a piezoelectric single crystal and which are different inthe direction of polarization from one another, and these plate-shapedmembers are joined with one another, respectively, to form thelayer-shaped parts.

[0055] And in a particularly preferred embodiment, the axial directionof polarization in one layer-shaped part of at least one main face sideand the axial direction of polarization in the other layer-shaped partof the other main face side are reverse to each other.

[0056] Although a piezoelectric single crystal which is a material forthe vibrator is not limited in particular, it is particularly preferablethat a single crystal is quartz, lithium niobate, lithium tantalate, asolid solution of lithium niobate-lithium tantalate, langasite, orlithium tetraborate, and it is more preferable that a single crystal islithium niobate, lithium tantalate, a solid solution of lithiumniobate-lithium tantalate, or langasite. Among the above-mentionedsingle crystals, single crystals of quartz, LiNbO₃, LiTaO₃, and (Li(Nb,Ta)O₃ have particularly large electromechanical coupling coefficients.Comparing a single crystal of LiNbO₃ and a single crystal of LiTaO₃ witheach other, the single crystal of LiTaO₃ has a larger electromechanicalcoupling coefficient and a better thermal stability than the singlecrystal of LiNbO₃.

[0057] And it is possible to exemplify lead zirconate titanate (PZT),relaxer compounds (general expression: Pb(A1/3B2/3)O3 where A is Cd, Zn,Mg or the like, and B is Nb, Ta, W or the like), a piezoelectric singlecrystal of a mixed crystal system of lead zirconate titanate and arelaxer compound, langasite, and lithium tetraborate.

[0058] A vibratory gyroscope of a sixth embodiment of the invention is avibratory gyroscope using a vibrator which is composed of plural armsand a base part for joining the plural arms with it, gives a drivevibration in a specified plane to the arms, and obtains a turningangular rate from a detection vibration corresponding to the appliedangular rate of turning, said vibratory gyroscope supporting thevibrator at a small domain where there is locally a domain having thesmallest detection vibration.

[0059] The invention can fix a domain where movement of the vibrator isthe smallest by supporting the vibrator at a small domain where there islocally a domain having the smallest detection vibration in case ofsupporting the vibrator. Accordingly, since it is possible toeffectively generate a detection vibration by means of a Coriolis force,a Q value of the detection vibration becomes high and the sensitivitycan be improved. Since the detection vibration generated by the Coriolisforce is small in amplitude, the invention is particularly effective toimprove the sensitivity.

[0060] And since it increases not only the Q value of detectionvibration but also the Q value of drive vibration and furthermore canimprove also the sensitivity to support a vibrator at a small domainwhere there is locally a domain having the smallest detection vibrationand a small domain where there is locally a domain having the smallestdrive vibration coincide with each other, it is preferable as apreferred embodiment to support the vibrator in this way. Furthermore,it is preferable to use as a material for a vibrator a piezoelectricmaterial such as piezoceramic or a single crystal of quartz, LiTaO₃,LiNbO₃, or the like, and it is more preferable in particular to use asingle crystal of quartz, LiTaO₃, LiNbO₃, or the like. The reason isthat a high Q value of a single crystal itself can be effectively used.

[0061] In the present invention, a small domain where there is locally adomain having the smallest detection vibration or the smallest drivevibration is a domain within a range where the amplitude of detectionvibration or drive vibration is smaller than a thousandth of the maximumamplitude in a vibrator.

[0062] A vibratory gyroscope of a seventh embodiment of the invention isa vibratory gyroscope having a vibrator composed of an arm of apiezoelectric member, wherein said arm has a hollow part and a pair ofelectrodes are provided on each of the parts between which the hollowpart of the arm is disposed.

[0063] In this invention, to provide a pair of electrodes on each of theparts between which the hollow part of the arm is disposed prevents anunnecessary displacement from being generated by an electric fieldflowing from one pair of electrodes to the other pair of electrodes,since there is no piezoelectric member at that place. Accordingly, sincenoises can be removed, it is possible to make a high-accuracy angularspeed detection.

[0064] Although the hollow part is not limited in size in particular, itis preferable to form the hollow part equal to or longer than theelectrode in the longitudinal direction of the electrode, because aleakage electric field does not cause an unnecessary displacement of thearm at all since there is no piezoelectric member to contribute thedisplacement. And since it is necessary to provide the hollow partcorrespondingly to the electrodes, it is preferable to provide thehollow part at a range of ⅓ to ⅔ arm length distant from the base of thearm in the arm of this invention which is more curved at a positioncloser to its base and in which each of the electrodes needs to beprovided at a range of ⅓ to ⅔ arm length distant from the arm base.Furthermore, it is preferable to use a 130-degree Y plate of lithiumtantalate (LiTaO₃) as a piezoelectric member, since to provide thehollow part of the invention is very effective to a large influence of aleakage electric field which this invention takes as a problem.

[0065] In each of the above vibrators, its main surface may preferablyhave a flatness of not larger than 100 μm, and an angle at the main partand the bending-vibration piece may preferably be not smaller than 45°.

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The file of this patent contains at least one drawing executed incolor. Copies of this patent with color drawing(s) will be provided bythe Patent and Trademark Office upon request and payment of thenecessary fee.

[0067]FIG. 1 is a perspective view showing a configuration of a formervibrator;

[0068]FIG. 2 is a perspective view showing a configuration of a formervibrator;

[0069] FIGS. 3 to 23 relate to a first embodiment of the presentinvention;

[0070]FIG. 3 is a front view of a vibratory gyroscope of an embodiment;

[0071]FIG. 4(a) is a front view for explaining a vibration direction ofa linear vibrator;

[0072]FIG. 4(b) is a front view for explaining a drive direction of thevibrator of FIG. 3;

[0073] FIGS. 5(a), 5(b) and 5(c) are schematic diagrams for explainingvibration directions of the respective parts of the vibrator of FIG. 3and the principle of vibration of it;

[0074]FIG. 6 is a front view of a vibratory gyroscope using a fixingpiece part;

[0075]FIG. 7 is a front view of another vibratory gyroscope using afixing piece part;

[0076]FIG. 8 is a front view of a further other vibratory gyroscopeusing a fixing piece part;

[0077]FIG. 9 is a front view showing a vibrator whose bending-vibrationpieces are not perpendicular to a base part;

[0078]FIG. 10 is a front view showing a vibrator whose bending-vibrationpieces are curved in shape;

[0079]FIG. 11 is a front view of a vibrator having a projection 35projecting further from its bending-vibration piece;

[0080]FIG. 12 is a perspective view roughly showing a vibratorygyroscope using a vibrator comprising a main arm 101F and a pair ofresonate arms;

[0081]FIG. 13(a) is a diagram showing the form of a drive vibration ofthe vibrator of FIG. 11;

[0082] FIGS. 13(b) and 13(c) are diagrams showing the form of adetection vibration of the vibrator of FIG. 11;

[0083]FIG. 14 is a perspective view roughly showing a vibratorygyroscope using a vibrator comprising a main arm 101G and a pair ofresonate arms;

[0084]FIG. 15 is a perspective view roughly showing a vibratorygyroscope using a vibrator comprising a main arm 101H and a pair ofresonate arms, both sides of which are different in size;

[0085]FIG. 16 is a perspective view of the vibratory gyroscope of FIG.15;

[0086]FIG. 17 is a graph showing a relation between dimension a andvariation in the natural frequencies of a drive vibration and a spuriousvibration of the vibratory gyroscope shown in FIGS. 15 and 16;

[0087]FIG. 18 is a perspective view roughly showing a vibratorygyroscope provided with a main arm 101I and a pair of resonant arms,wherein a voltage applying direction to the main arm and a voltageapplying direction to the resonant arms make an angle of 120 degreeswith each other;

[0088]FIG. 19 is a perspective view roughly showing a vibratorygyroscope provided with a main arm 101J and a pair of resonant arms,wherein a voltage applying direction to the main arm and a voltageapplying direction to the resonant arms make an angle of 120 degreeswith each other;

[0089]FIG. 20 is a perspective view roughly showing a vibratorygyroscope provided with a main arm 101N and a pair of resonant arms,wherein a voltage applying direction to the main arm and a voltageapplying direction to the resonant arms make an angle of 15 degreesrespectively to axes a;

[0090]FIG. 21 is a perspective view roughly showing a vibratorygyroscope using a vibrator provided with a main arm 101K and a pair ofresonant arms, wherein each of the bending-vibration piece and theresonant arms is provided with a through hole;

[0091]FIG. 22 is a perspective view roughly showing a vibratorygyroscope using a vibrator provided with a main arm 101L and a pair ofresonant arms, wherein each of the bending-vibration piece and theresonant arms is provided with a through hole;

[0092]FIG. 23 is a perspective view roughly showing a vibratorygyroscope using a vibrator provided with a fixing piece part 12, a mainarm 101L, a pair of resonant arms 92A and 92B, a resonant piece 103, anda pair of second resonant arms 97A and 97B;

[0093] FIGS. 24 to 27 relate to a second embodiment of the presentinvention;

[0094]FIG. 24 is a figure showing a configuration of an example of avibrator of the invention;

[0095]FIG. 25 is a figure showing a configuration of another example ofa vibrator of the invention;

[0096]FIG. 26 is a figure showing a configuration of a further otherexample of a vibrator of the invention;

[0097]FIG. 27 is a figure showing a configuration of a still furtherother example of a vibrator of the invention;

[0098] FIGS. 28 to 34 relate to a third embodiment of the presentinvention;

[0099]FIG. 28 is a figure showing a configuration of an example of avibrator of the invention;

[0100]FIG. 29(a) and (b) are diagrams for explaining a drive vibrationand a detection vibration in a vibrator of the invention;

[0101]FIG. 30 is a figure showing a configuration of another example ofa vibrator of the invention;

[0102]FIG. 31 is a figure showing a configuration of a further otherexample of a vibrator of the invention;

[0103]FIG. 32 is a figure showing a configuration of a still furtherother example of a vibrator of the invention;

[0104]FIG. 33 is a figure showing a configuration of a still furtherother example of a vibrator of the invention;

[0105]FIG. 34 is a figure showing a configuration of a still furtherother example of a vibrator of the invention;

[0106] FIGS. 35 to 43 relate to a fourth embodiment of the presentinvention;

[0107]FIG. 35 is a figure showing a configuration of an example of avibrator used in the invention;

[0108]FIG. 36 is a figure showing a configuration of another example ofa vibrator used in the invention;

[0109]FIG. 37 is a figure showing a configuration of a further otherexample of a vibrator used in the invention;

[0110]FIG. 38 is a figure showing a configuration of a still furtherother example of a vibrator used in the invention;

[0111]FIG. 39 is a block diagram showing an example of a phasedifference detecting means in a vibratory gyroscope of the invention;

[0112]FIG. 40 is a graph showing an example of a relation between aphase difference and a turning angular rate in case that a leakagesignal and a gyroscopic signal have a specified relation between them inthe invention;

[0113]FIG. 41 is a graph showing another example of a relation between aphase difference and a turning angular rate in case that a leakagesignal and a gyroscopic signal have a specified relation between them inthe invention;

[0114]FIG. 42 is a graph showing a further other example of a relationbetween a phase difference and a turning angular rate in case that aleakage signal and a gyroscopic signal have a specified relation betweenthem in the invention;

[0115]FIG. 43 is a graph showing a relation between a linearity errorand the ratio of a leakage signal to a gyroscopic signal in theinvention;

[0116] FIGS. 44 to 59 relate to a fifth embodiment of the presentinvention;

[0117]FIG. 44 is a perspective view of a tuning-fork vibrator studied bythe inventors;

[0118]FIG. 45(a) is a plan view for explaining a method for excitingvibration in vibration arms;

[0119]FIG. 45(b) is a front view of each vibration arm taken in thedirection of the X axis;

[0120]FIG. 46 is a perspective view showing a vibrator 156 of avibratory gyroscope of an embodiment of the invention;

[0121]FIG. 47(a) is a plan view for explaining a method for excitingvibration in a plane-normal vibration arm of a vibrator of an embodimentof the invention;

[0122]FIG. 47(b) is a front view of the vibration arm taken in thedirection of the X axis;

[0123]FIG. 48 is a schematic plan view for showing a plane-parallelvibration excited in a plane-parallel vibration arm;

[0124]FIG. 49(a) is a plan view for explaining a method for excitingvibration in a plane-normal vibration arm of a vibrator of anotherembodiment of the invention;

[0125]FIG. 49(b) is a front view of the plane-normal vibration arm takenin the direction of the X axis;

[0126]FIG. 50(a) is a plan view for explaining a method for excitingvibration in a plane-normal vibration arm of a vibrator of a furtherother embodiment of the invention;

[0127]FIG. 50(b) is a front view of the plane-normal vibration arm takenin the direction of the X axis;

[0128]FIG. 51 is a perspective view showing a three-forked tuning-forkvibrator of a vibratory gyroscope of the invention;

[0129]FIG. 52 is a perspective view showing a three-forked tuning-forkvibrator of a vibratory gyroscope of another embodiment of theinvention;

[0130]FIG. 53 is a perspective view showing a three-forked tuning-forkvibrator of a vibratory gyroscope of a further other embodiment of theinvention;

[0131]FIG. 54(a), 54(b) and 54(c) are perspective views showing basemembers 185A, 185B and 185C, respectively;

[0132]FIG. 55 is a perspective view showing a three-forked tuning-forkvibrator of a vibratory gyroscope of a still further other embodiment ofthe invention;

[0133]FIG. 56 is a plan view schematically showing the form ofplane-normal vibration arms 188A and 188B;

[0134]FIG. 57 is a plan view schematically showing the form ofplane-normal vibration arms;

[0135]FIG. 58 is a plan view schematically showing the form ofplane-normal vibration arms of another embodiment;

[0136]FIG. 59 is a plan view schematically showing the form ofplane-parallel vibration arms of another embodiment;

[0137] FIGS. 60 to 67 relate to a sixth embodiment of the presentinvention;

[0138]FIG. 60(a), 60(b) and 60(c) are figures showing a configuration ofan example of a vibrator of a vibratory gyroscope of the invention;

[0139]FIG. 61(a) and 61(b) are figures showing an example of a methodfor supporting a vibrator in the invention;

[0140]FIG. 62 is a color micrograph showing an example of a result of anatural mode analysis of a tuning-fork vibrator by means of a finiteelement method;

[0141]FIG. 63 is a color micrograph showing another example of a resultof a natural mode analysis of a tuning-fork vibrator by means of afinite element method;

[0142]FIG. 64 is a color micrograph showing an example of a result of anatural mode analysis of a vibrator having a T-shaped arm by means of afinite element method;

[0143]FIG. 65 is a color micrograph showing an example of a result of anatural mode analysis of a vibrator having a Y-shaped arm by means of afinite element method;

[0144]FIG. 66 is a color micrograph showing an example of a result of anatural mode analysis of a vibrator having opposite Y-shaped arms bymeans of a finite element method;

[0145]FIG. 67 is a color micrograph showing another example of a resultof a natural mode analysis of a vibrator having opposite Y-shaped armsby means of a finite element method;

[0146] FIGS. 68 to 74 relate to a seventh embodiment of the presentinvention;

[0147]FIG. 68 is a figure showing a configuration of an example of avibratory gyroscope of the prior art;

[0148]FIG. 69 is a figure showing a configuration of an example of avibration arm in the former example shown in FIG. 68;

[0149]FIG. 70 is a figure for explaining a problem in the vibration armof the former example shown in FIG. 68;

[0150]FIG. 71 is a figure showing a configuration of an example of avibratory gyroscope of the invention;

[0151]FIG. 72 is a figure showing a configuration of an example of avibration arm in the example shown in FIG. 71;

[0152]FIG. 73 is a figure showing a configuration of another example ofa vibratory gyroscope of the invention;

[0153]FIG. 74 is a figure showing a configuration of an example of avibration arm in the example shown in FIG. 73,

[0154]FIG. 75 is a front view showing a vibrator according to anembodiment of the invention;

[0155]FIG. 76 is a front view showing a vibrator according to anotherembodiment of the invention;

[0156] FIGS. 77(a) and 77(b) are partial front views showing alternativethrough holes and/or hollow portions;

[0157]FIG. 78 is a front view showing a vibrator according to anotherembodiment of the invention;

[0158]FIG. 79 is a front view showing a vibrator according to anotherembodiment of the invention;

[0159]FIG. 80 is a front view showing a vibrator according to anotherembodiment of the invention;

[0160]FIG. 81 is an enlarged view of circled region A from FIG. 80;

[0161]FIG. 82 is a front view showing a vibrator according to anotherembodiment of the invention; and

[0162]FIG. 83 is a front view showing a vibrator according to anotherembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0163] A first preferred embodiment of the present invention isdescribed with reference to the drawings in the following. FIG. 3 is afront view showing a vibrator of an embodiment of the invention, FIG.4(a) is a front view for explaining a direction of vibration of a linearvibrator, FIG. 4(b) is a front view for explaining a direction ofvibration of the vibrator of FIG. 3, and FIGS. 5(a), 5(b) and 5(c) areschematic diagrams for explaining vibration directions of the respectiveparts of the vibrator of FIG. 3 and the principle of vibration of it.

[0164] In a main arm 101A of a vibrator 2 of FIG. 3, a base part 3extends from and perpendicularly to a fixing part 1, and one end part 3a of the base part 3 is fixed on the fixing part 1. Specified excitingmeans 5A and 5B are provided in the base part 3. Two bending-vibrationpieces 4A and 4B extending perpendicularly to the base part 3 areprovided at the other end part 3 b of the base part 3.

[0165] A vibration mode of this vibrator 2 is described. Asschematically shown in FIG. 5(a), the base part 3 is bent in thedirection of arrow H around a joint 26 of it and the fixing member 1 byapplying a drive voltage to the exciting means 5A and 5B. With thisbending, not only the base part 3 of the vibrator 2 but also each pointof the bending-vibration pieces 4A and 4B are moved as shown by arrow I.A velocity vector of this movement is assumed as V.

[0166] In this embodiment, the Z axis is the axis of turning, and thevibrator 2 is turned around the Z axis. For example, when the vibrator 2is moved in the direction of arrow H and the whole vibrator 2 is turnedaround the Z axis as shown by arrow w, a Coriolis force acts as shown byarrow J. As a result, as shown in FIG. 5(b), the bending-vibrationpieces 4A and 4B are bent in the direction of arrow J around a joint 25of the other end part 3 b of the base part 3 and the bending-vibrationpieces.

[0167] On the other hand, as shown in FIG. 5(c), when the base part 3 isdriven in the direction of arrow K and the whole vibrator 2 is turnedaround the Z axis as shown by arrow ω, a Coriolis force acts as shown byarrow L. As a result, the bending-vibration pieces 4A and 4B are bent inthe direction of arrow L around the joint 25 of the other end part 3 bof the base part 3 and the bending-vibration pieces. In this way, thebending-vibration pieces 4A and 4B can be vibrated as shown by arrows Aand B.

[0168] In this way, it is possible to convert a Coriolis force generatedin the X-Y plane in the bending-vibration pieces 4A and 4B to a bendingvibration around the joint 25 of the bending-vibration pieces 4A and 4B,and obtain a turning angular rate on the basis of the bending vibration.Thanks to this, even in case that the vibrator is arrangedperpendicularly to the axis Z of turning (horizontally arranged), aturning angular rate can be detected in high sensitivity.

[0169] The sensitivity of detection by the vibrator 2 shown in FIGS. 3and 5 is furthermore described. As shown in FIG. 4(a), the inventors usea vibrator 8A and 8B in the shape of a long and narrow stick, set thevibrator 8B in the X-Y plane, and extend and contract it. Hereupon, 8Arepresents a state where the vibrator is extended and 8B represents astate where the vibrator is contracted. Hereupon, a moment when thevibrator is going to extend as shown by arrow E toward the state 8A fromthe state 8B is considered. When the vibrator 8B is turned around the Zaxis, a Coriolis force acts as shown by arrow F. However, sincedisplacement of such a piezoelectric member caused by longitudinalvibration is small and its resonance frequency is low, the sensitivitycannot be made high.

[0170] On the other hand, as shown in FIG. 4(b), the invention vibratesthe base part 3 as shown by arrow G and thus vibrates thebending-vibration pieces 4A and 4B as shown by arrow D. In this way, itis possible to obtain a much larger amplitude, a much larger vibrationspeed and a greater Coriolis force than the case of FIG. 4(a).

[0171] And in case of using the vibrator shown in FIGS. 3 and 5, it ispossible to excite a bending vibration in the bending-vibration pieces4A and 4B as shown by arrows A and B. When the vibrator 2 turns in theX-Y plane, a Coriolis force is applied to each of the bending-vibrationpieces and the Coriolis forces of the bending-vibration pieces areapplied to the base part 3. By this, the base part 3 performs a bendingvibration around the joint 26 as shown by arrow G. It is possible todetect the bending vibration of the base part 3 and output a signalaccording to the detected bending vibration.

[0172] In case of forming the vibrator out of a piezoelectric singlecrystal, electrodes are used as exciting means and detecting means 5A,5B, 6A, 6B, 6C and 6D. However, the vibrator can be formed out of anelastic material, and in this case, piezoelectric members provided withelectrodes can be used as exciting means and detecting means 5A, 5B, 6A,6B, 6C and 6D. And in case that there is one of the exciting means (ordetecting means) 5A and 5B, at least one of excitation and detection ofvibration can be performed. And in case that there is one of thedetecting means (or exciting means) 6A, 6B, 6C and 6B, at leastexcitation (or detection) of vibration can be performed.

[0173] In embodiments shown in FIGS. 6 to 8, a main arm is provided atone side of a fixing piece part both ends of which are fixed, a resonantpiece is provided at the other side of the fixing piece part, and thefixing piece part, the main arm and the resonant piece are formed so asto extend substantially in a specified plane.

[0174] In the embodiment of FIG. 6, an exciting means side and adetecting means side are separated by a fixing piece part 12.Concretely, both ends of the fixing piece part 12 are fixed by fixingmembers 11. A main arm 101B is provided at one side of the fixing piecepart 12. The main arm 101B is provided with a long and narrow base part16 and two bending-vibration pieces 4A and 4B extending from an end part16 b of the base part 16 in a direction perpendicular to thelongitudinal direction of the base part 16.

[0175] A resonant piece 32 is provided at the other side of the fixingpiece part 12. The resonant piece 32 is provided with a rectangularsupporting part 13 extending from and perpendicularly to the fixingpiece part 12, and specified exciting means 5A and 5B are provided inthe supporting part 13. Two vibration pieces 15A and 15B extendingperpendicularly to the supporting part 13 are provided at the other end13 b side of the supporting part 13. The end part 16 a of the base part16 and the end part 13 a of the supporting part 13 are joined to thefixing piece part 12. In this way, both sides of the fixing piece part12 are nearly line-symmetric to each other.

[0176] A vibration mode of this vibrator 10 is described. By applying adriving voltage to the exciting means 5 a and 5B, the supporting part 13and the pair of vibration pieces 15A and 15B are vibrated around thejoint 27 of the fixing piece part 12 and the supporting part 13 as shownby arrow M. In resonance with this vibration, the base part 16 and thepair of vibration pieces 4A and 4B are vibrated around the joint 26 ofthe fixing part 12 and the base part 16 as shown by arrow D.

[0177] When the whole of this vibrator 10 is turned around the axis Z ofturning, a Coriolis force acts on each of the bending-vibration pieces4A and 4B as described above. As the result, the bending-vibrationpieces 4A and 4B are vibrated around the joint 25, respectively, asshown by arrows A and B.

[0178] In this way, it is possible to convert a Coriolis force generatedin the X-Y plane in the bending-vibration pieces 4A and 4B by thebending vibration of the resonant piece 32 to a bending vibration aroundthe joint 25 of the bending-vibration pieces 4A and 4B, and obtain aturning angular rate on the basis of this bending vibration. Thanks tothis, even in case that the vibrator is arranged perpendicularly to theaxis Z of turning (horizontally arranged), a turning angular rate can bedetected in high sensitivity.

[0179] In the embodiment of FIG. 6, in the vibrator 10, the resonantpiece 32 and the main arm 101B are mirror-symmetric in shape to eachother in relation to the fixing piece part 12, and by this the naturalresonance frequencies of the respective vibration modes of the resonantpiece and the main arm are matched with each other. However, it is notnecessary that the resonant piece 32 and the main arm 101B areline-symmetric in shape to each other in relation to the fixing piecepart 12.

[0180] In a vibrator 20 of FIG. 7, since a main arm 101B composed of abase part 16 and a pair of bending-vibration pieces 4A and 4B, and afixing piece part 12 are the same in shape as those shown in FIG. 6,description of them is omitted. A long and narrow rectangular resonantpiece 21 extends from the fixing piece part 12 perpendicularly to it.Exciting means 5A and 5B are provided near an end part 21 a at thefixing piece part 12 side of the resonant piece 21.

[0181] By applying a driving voltage to the exciting means SA and 5B,the resonant piece 21 is vibrated around the joint 27 of it and thefixing piece part 12 as shown by arrow M. In resonance with thisvibration, the base part 16 and the pair of bending-vibration pieces 4Aand 4B are vibrated around the joint 26 of them and the fixing member 11as shown by arrow D.

[0182] In this way, the whole vibrator is more simplified in structurein comparison with the embodiment of FIG. 6 by forming the resonantpiece 21 into a long and narrow rectangle. So as not to make large afrequency difference between the vibration frequency at the excitingside and the vibration frequency at the detection side of the fixingpiece part 12, it is necessary to adjust both sides so that they arenearly equal in moment to each other. Comparing the resonant piece 21 ofFIG. 7 with the resonant piece 32 of FIG. 6 from this viewpoint, in FIG.7 there are no vibration pieces 15A and 15B, and there are no weightsfor them. Therefore, it is necessary that the height of the top end 21 bof the resonant piece projecting from the fixing piece part 12 is higherthan the height of the resonant piece 32 projecting from the fixingpiece part 12, namely, that the resonant piece 21 is heavier in weightthan the supporting part 13. Accordingly, the resonant piece 21projecting from the fixing piece part 12 tends to increase in height.

[0183] In a vibrator 22 of FIG. 8, since a main arm 101B composed of abase part 16 and a pair of bending-vibration pieces 4A and 4B, and thefixing piece part 12 are the same in shape as those shown in FIG. 6,description of them is omitted. A resonant piece 31 is provided on thefixing piece part 12. The resonant piece 31 is provided with arectangular supporting part 30 extending from the fixing piece part 12perpendicularly to it, and the supporting part 30 is provided withexciting means 5A and 5B. An expanded part 23 in the shape of a broadrectangle is formed at the top end side of the supporting part 30.

[0184] By applying a driving voltage to the exciting means 5A and 5B,the resonant piece 31 is vibrated around the joint 27 of it and thefixing piece part 12 as shown by arrow M. In resonance with thisvibration, the base part 16 and the pair of bending-vibration pieces 4Aand 4B are vibrated around the joint 26 of them and the fixing piecepart 12 as shown by arrow D.

[0185] In this way, by providing the expanded part 23 in the resonantpiece 31, it is possible to make lower in height the resonant piece 31projecting from the fixing piece part 12 and furthermore make avibration frequency of the resonant piece 31 closer to a vibrationfrequency of the base part 16 and bending-vibration pieces 4A and 4Bside.

[0186] In vibrators of the present invention, the longitudinal directionof a bending-vibration piece and the longitudinal direction of a basepart do not have to be necessarily perpendicular to each other. And abending-vibration piece may be straight or curved in shape. In case thata pair of bending-vibration pieces are provided, however, it ispreferable that both of them have mirror-symmetry to each other inrelation to the base part.

[0187] In a main arm 101C of a vibrator 40 of FIG. 9, bending-vibrationpieces 33A and 33B intersect the extending direction of a base part 3 ata specified angle θ. Although the intersecting angle is not a rightangle, the intersecting angle is preferably 45° to 135°, and it isparticularly preferably 70° to 100°. Due to this, the natural resonancefrequencies of vibration modes of vibrations N and P of thebending-vibration pieces 33A and 33B vary slightly in comparison withthe natural resonance frequency of the vibration mode of thebending-vibration piece of the vibrator shown in FIG. 3.

[0188] In a main arm 101D of a vibrator 41 of FIG. 10, bending-vibrationpieces 34A and 34B are in the shape of a slightly curved arc. Due tothis, the natural resonance frequencies of vibration modes of vibrationsQ and R of the bending-vibration pieces 34A and 34B vary slightly incomparison with the vibrator shown in FIG. 9. The shapes as shown inFIGS. 9 and 10 can be adopted also in the vibrators shown in FIGS. 6, 7,and 8.

[0189] Generally in a piezoelectric vibratory gyroscope, in order tokeep a good measurement sensitivity, it is required to keep a constantvibration frequency difference between the natural resonance frequencyof a drive vibration mode and the natural resonance frequency in adetection vibration mode. In vibrators of the present invention, whenthe natural resonance frequency of a vibration mode of a base part andthe natural resonance frequency of a vibration mode of abending-vibration piece become close to each other, the sensitivitybecomes good but the response speed is deteriorated. When a frequencydifference between the natural resonance frequency of a vibration modeof a base part and the natural resonance frequency of a vibration modeof a bending-vibration piece becomes large, the response speed becomesgood but the sensitivity is deteriorated.

[0190] Due to this, by removing a weight at the top end of thebending-vibration piece, it is possible to vary the natural resonancefrequency of a vibration mode of the bending-vibration piece. And byproviding a projection projecting from the bending-vibration piece atthe opposite side to the fixed end part of the base part and removing aweight of this projection, it is possible to vary the natural resonancefrequency of a vibration mode of the base part.

[0191] For example, in a main arm 101E of a vibrator 42 of FIG. 11, aprojection 35 projecting from bending-vibration pieces 4A and 4B isprovided at the other end part 3 b side of the base part 3. And thenatural resonance frequency of a vibration mode of vibration D of thebase part is varied by performing a process of removing a weight from apart 37 of the projection 35. And the natural resonance frequencies ofvibration modes of vibrations A and B of the bending-vibration pieces 4Aand 4B can be varied independently of each other by performing a processof removing weights from the top ends 36A and 36B of thebending-vibration pieces 4A and 4B. This removing process can beperformed by a laser irradiation process or a machining process.

[0192] Next, an embodiment in which a vibrator of the invention isprovided with at least a pair of resonant pieces which resonate withvibration of the base part and project from the fixing part isdescribed.

[0193] As shown in FIGS. 3 to 11, a vibratory gyroscope utilizing abending vibration of a main arm or a resonant piece can attain such ahigh sensitivity that it cannot be obtained up to now in case ofadopting a vibrator extending perpendicularly to a turning system. As aresult of a further study of the inventors, however, it has been foundthat the following problem remains. That is to say, since a main armcomposed of a bending-vibration piece and a base part is formed so as toproject from a fixing part, for example, in case of using a bendingvibration of the bending-vibration piece as a drive vibration anddetecting a bending vibration around the fixing part of the base part,it has been found that the vibration of the base part is apt to dampcomparatively soon and there is room for improvement in the Q value ofthe detection vibration.

[0194] As a result of study for solving this problem, the inventors havethought of projecting at least one pair of resonant arms together with abase part from a fixing part and resonating the resonant arms withvibration of the base part. In this case, although it is possible to usevibration of the resonant arms and the base part as a drive vibration,it is more preferable to use vibration of the resonant arms and the basepart as a detection vibration. Since a detection vibration bearing agyroscopic signal is much smaller in amplitude than a drive vibration, agreater effect of improvement of the Q value can be obtained.

[0195] FIGS. 12 to 14 show vibratory gyroscopes of such embodiments.

[0196] In a vibrator 44 of a vibratory gyroscope 43 of FIG. 12, a mainarm 101F projects from a fixing part 1, and a pair of resonant arms 48Aand 48B project at both sides of the main arm 101F. A base part 3projects from the fixing part 1, bending-vibration pieces 45A and 45Bextending perpendicularly to the base part 3 are formed at an end part 3b side of the base part 3, and weights 47A and 47B are formed at the topends of the bending-vibration pieces 45A and 45B. The bending-vibrationpieces 45A and 45B are provided, respectively, with exciting means(detecting means) 46A, 46B, 46C and 46D.

[0197] The resonant arms 48A and 48B projecting from the fixing part 1are provided, respectively, with detecting means (exciting means) 49A,49B, 49C and 49D, and weights 50A and 50B are formed, respectively, atthe top ends of the resonant arms.

[0198] A preferable vibration mode in this case is described withreference to FIGS. 13(a) to 13(c). As described above, thebending-vibration pieces 45A and 45B are excited to bending-vibrate asshown by arrow S in FIG. 13(a). A Coriolis force acts as shown by arrowT when the whole vibrator is turned as described above. There are pluralvibrations excited in the base part and a pair of resonant arms by thisCoriolis force.

[0199]FIG. 13(b) shows the secondary vibrations. In this case, the basepart 3 and the resonant arms 45A and 45B are bending-vibrated reverselyin phase to each other, and simultaneously with this, thebending-vibration pieces 45A and 45B are vibrated so as to deviate froma straight line 58. FIG. 13(c) shows the primary vibrations. In thiscase, the base part 3 and the resonant arms 45A and 45B also arebending-vibrated reversely in phase to each other, and simultaneouslywith this, the bending-vibration pieces 45A and 45B also are vibrated soas to deviate from a straight line 58. The vibrations of thebending-vibration pieces 45A and 45B are reverse in phase to each other,respectively, in case of the primary vibrations and the secondaryvibrations.

[0200] Hereupon, although any of the primary vibration and the secondaryvibration may be used as a detection vibration, it is necessary toselect it so that a frequency difference between the natural resonancefrequency of a drive vibration and the natural resonance frequency of adetection vibration can be within a certain range.

[0201] In a vibrator 60A of a vibratory gyroscope 59A of FIG. 14, a mainarm 104G projects from a fixing part 1, a base part 3 projects from thefixing part 1, and bending-vibration pieces 61A and 61B extendingperpendicularly to the base part 3 are formed at an end part 3 b side ofthe base part 3. Since there are not parts corresponding to the weights47A and 47B, it is necessary to lengthen the bending-vibration piecesaccordingly. The bending-vibration pieces 61A and 61B are provided,respectively, with exciting means (detecting means) 46A, 46B, 46C and46D.

[0202] A pair of resonant arms 62A and 62B project from the fixing part1, and a resonant arms 62A and 62B are provided, respectively, withdetecting means (exciting means) 49A, 49B, 49C and 49D.

[0203] In this invention, in case of using resonant arms, it is possibleto vary the natural resonance frequency of vibration of a so-calledspurious mode by making different in projection height the resonant armsprojecting from both positions of the fixing part. This embodiment isdescribed with reference to a vibratory gyroscope 59B shown in FIGS. 15and 16.

[0204] In a vibrator 60B, a main arm 101H projects from a projection laof a fixing part 1. That is to say, a base part 3 projects, andbending-vibration pieces 61A and 61B extending perpendicularly to thebase part 3 are formed at an end part 3 b side of the base part 3. Thebending-vibration pieces 61A and 61B are provided, respectively, withdriving electrodes 46A, 46B, 46C and 46D. And a pair of resonant arms63A and 63B project from the fixing part 1, and the resonant arms 63Aand 63B are provided, respectively, with detecting electrodes 49A, 49B,49C and 49D.

[0205] In a perspective view of FIG. 16, the driving electrodes and thedetection electrodes are shown in cross-sectional views.

[0206] A cut-off part 74 of dimension a is provided outside each of theresonant arms, and by this a projection 1 a of a in height is projectedfrom the fixing part 1. As a result, it is possible to deviate thenatural resonance frequency of vibration of a spurious mode from thenatural resonance frequency of a drive vibration.

[0207] For example, in a vibrator shown in FIG. 15, in case of using abending vibration of the bending-vibration pieces 61A and 61B as a drivevibration, and adjusting its natural resonance frequency to 8750 Hz,bending vibrations of the resonant arms 63A and 63B reverse in phase toeach other as shown by arrow U in FIG. 15 are in a spurious mode.Natural resonance frequencies of these vibrations are 8700 Hz as shownin FIG. 17, in case of a=0 as shown in FIG. 14. As a result, since afrequency difference between the natural resonance frequency of thedrive vibration and the natural resonance frequency of the spurious modeis 50 Hz, a signal generated by the vibrations reverse in phase of theresonant arms is made much larger than a gyroscopic signal.

[0208] As shown in FIG. 17, however, the natural resonance frequency ofa spurious mode is greatly varied with the increase of height a.Particularly by making the a 1.0 mm or more, it is possible to greatlydeviate the natural resonance frequency of a spurious mode from thenatural resonance frequency of a drive vibration.

[0209] In this way, to make different in height the resonant armsprojecting from both positions of the fixing part is effective to reducenoises caused by vibration in a spurious mode, and for the purpose ofthis, the a is particularly preferably 1.0 mm or more. This ispreferably 6.0 mm or less.

[0210] In the vibratory gyroscopes of the embodiments described above,in case of forming a vibrator out of a piezoelectric single crystal,bending-vibration pieces, a base part or resonant arms arebending-vibrated by applying a voltage in the direction perpendicular tothe page face. Such a bending-vibration method for vibrating the arms isparticularly useful in case of using a single crystal, for example, oflithium niobate, lithium tantalate, or a solid solution of lithiumniobate-lithium tantalate.

[0211] As described above, however, the vibrators of the embodiments ofFIGS. 3 to 16 can be naturally applied also to another piezoelectricsingle crystal such as quartz crystal or the like as adopting the sameform of a drive vibration and a detection vibration. However, since thiscase is different in direction of an effective piezoelectric axis of thepiezoelectric single crystal from the case of lithium niobate and thelike, it is necessary to properly change the driving electrode and thedetection electrode in shape in order to utilize the effectivepiezoelectric axis for bending vibration.

[0212] FIGS. 18 to 20 all show vibratory gyroscopes of particularlypreferred embodiments in case that a vibrator is formed by using apiezoelectric single crystal having the triad axis of symmetry (a-axis)in a specified plane like a quartz crystal and its c-axis isperpendicular to the specified plane.

[0213] In such a form, it is preferable to set a voltage applyingdirection in a bending-vibration piece and a signal voltage direction ina resonant arm along the a-axis. FIGS. 18 and 19 relate to suchembodiments.

[0214] In a vibrator 60C of a vibratory gyroscope 59C of FIG. 18, a mainarm 101I and a base part 3 project from a fixing part 1, andbending-vibration pieces 64A and 64B extending perpendicularly to thebase part 3 are formed at an end part 3 b side of the base part 3. Thebending-vibration pieces 64A and 64B are provided, respectively, withdriving electrodes 65A and 65B. These drive electrodes are shaped asshown in a sectional view taken along A-A′, and the drive electrode 65Ais grounded and the drive electrode 65B is connected to analternating-current power source 68. By this, a voltage is applied inthe direction of the a-axis in the bending-vibration pieces 64A and 64B,and a bending vibration is generated.

[0215] The longitudinal directions of a pair of resonant arms 66A and66B are inclined at an angle of 120° to the bending-vibration pieces 64Aand 64B. The detection electrodes 67A and 67B in the resonant arms 66Aand 66B are the same in shape as the drive electrodes 65A and 65B. Asthe result, a voltage is applied in the direction of the a-axis also inthe resonant arms 66A and 66B. Therefore, both of a piezoelectricconstant utilized in a bending-vibration piece and a piezoelectricconstant utilized in a resonant arm are increased and come to the samedegree.

[0216] In a vibrator 60D of a vibratory gyroscope 59D of FIG. 19, a mainarm 101J and a base part 3 project from a fixing part 1, andbending-vibration pieces 70A and 70B extending in the directionsinclined at an angle of 120° to the base part 3 are formed at an endpart 3 b side of the base part 3. Weights 71A and 71B are provided,respectively, at the ends of the bending-vibration pieces 70A and 70B.

[0217] The bending-vibration pieces 70A and 70B are provided,respectively, with drive electrodes 72A and 72B. These drive electrodesare shaped as shown in a sectional view taken along A-A′, and the driveelectrode 72B is grounded and the drive electrode 72A is connected to analternating-current power source 68. By this, a voltage is applied inthe direction of the a-axis in the bending-vibration pieces 70A and 70B,and a bending vibration is generated.

[0218] The longitudinal direction of a pair of resonant arms 75A and 75Bis inclined at an angle of 120° to the bending-vibration pieces 70A and70B. The shape of the detection electrodes 76A, 76B, 76C and 76D isshown in a sectional view taken along B-B′, and the detection electrodes76D are grounded and a detection signal is taken out from the detectionelectrodes 76C. As the result, a signal voltage is generated in thedirection of the a-axis also in the resonant arms 75A and 75B.

[0219] As shown in the embodiment of FIG. 20 for example, in case ofextending a bending-vibration arm and resonant arms in the verticaldirection, a detection signal can be taken out by inclining thelongitudinal directions of the bending-vibration arm and the resonantarms at an angle of 10° to 20°, preferably 15° to the a-axis.

[0220] That is to say, in a vibrator 60H of a vibratory gyroscope 59H, amain arm 101N and a base part 3 project from a fixing part 1, andbending-vibration pieces 99A and 99B extending perpendicularly to thebase part 3 are formed at an end part 3 b side of the base part 3, andweights 47A and 47B are provided, respectively, at the top ends of thebending-vibration pieces. The bending-vibration pieces are provided,respectively, with drive electrodes 65A and 65B. And a pair of resonantarms 100A and 100B project from the fixing part 1 in parallel with thebase part 3, and the resonant arms 100A and 101B are provided,respectively, with detection electrodes 67A and 67B.

[0221] Hereupon, both of a voltage applying direction in thebending-vibration pieces and a signal voltage direction in the resonantarms form an angle of 15° with the a-axis, and therefore, the samepiezoelectric constant is utilized in both arms.

[0222] In this invention, each of the bending-vibration pieces or theresonant arms can be provided with a through hole extending in itslongitudinal direction. Thanks to this, the sensor sensitivity can beimproved by lowering the natural resonance frequency of thebending-vibration pieces or the resonant arms and increasing theamplitude of the resonant arms. FIGS. 21 and 22 show vibratorygyroscopes of such embodiments of the invention.

[0223] In a vibrator 60E of a vibratory gyroscope 59E of FIG. 21, a mainarm 101K projects from a fixing part 1 and a base part 3 projects from afixing part 1, and bending-vibration pieces 78A and 78B extendingperpendicularly to the base part 3 are formed at an end part 3 b side ofthe base part 3. Weights 47A and 47B are provided, respectively, at thetop ends of the bending-vibration pieces. Through holes 79A and 79Bextending in the longitudinal direction of the bending-vibration piecesare formed, respectively, in the bending-vibration pieces. And long andnarrow drive electrodes 80A, 80B, 80C and 80D are provided,respectively, at both sides of the through holes of thebending-vibration pieces.

[0224] In this embodiment, a 130° Y plate of lithium tantalate is usedand the c-axis forms an angle of 50° with the main face of the vibrator.The vibrator has the best temperature characteristics at this angle. Inthe bending-vibration pieces, as shown in a sectional view taken alongA-A′, since a voltage applying direction to the drive electrodes 80A and80C, and a voltage applying direction to the drive electrodes 80B and80D are reverse to each other, the bending-vibration pieces are bent.

[0225] A pair of resonant arms 81A and 81B project from a fixing part 1and the resonant arms 81A and 81B are provided, respectively, withdetection electrodes 83A, 83B, 83C and 83D. Through holes 82A and 82Bextending in the longitudinal direction of the resonant arms are formed,respectively, in the resonant arms. And long and narrow detectionelectrodes 83A, 83B, 83C and 83D are provided, respectively, at bothsides of the through holes in the resonant arms. In the resonant arms,as shown in a sectional view taken along B-B′, a voltage generated inthe detection electrodes 83A and 83C, and a voltage generated in thedetection electrodes 83B and 83D are reverse to each other.

[0226] In a vibrator 60F of a vibratory gyroscope 59F of FIG. 22, a mainarm 101L and a base part 3 project from a fixing part 1, and a pair ofbending-vibration pieces 85A and 85B are formed at an end part 3 b sideof the base part 3, and weights 71A and 71B are provided, respectively,at the top ends of the bending-vibration pieces. Each of thebending-vibration pieces extends in the direction forming an angle of120° to the base part. Through holes 86A and 86B extending in thelongitudinal direction of the bending-vibration pieces are formed,respectively, in the bending-vibration pieces. And drive electrodes 89Aand 89D are provided on the outside walls of each of the through holes,and drive electrodes 89B and 89C are provided on the inside walls ofeach of them.

[0227] In this embodiment, a piezoelectric single crystal plate havingthe a-axis of the triad axis of symmetry in a specified plane likequartz crystal is used. In each of the bending-vibration pieces, asshown in a sectional view taken along A-A′, the drive electrodes 89A and89D on the outside walls are connected to an alternating-current powersource 68, and the drive electrodes 89B and 89C on the inside walls aregrounded. Since a combination of the drive electrodes 89A and 89B and acombination of the drive electrodes 89C and 89D have voltage applyingdirections reverse in phase to each other, the bending-vibration piecesare bent.

[0228] A pair of resonant arms 87A and 87B project from a projection 1 aof a fixing part 1 and through holes 88A and 88B extending in thelongitudinal direction of the resonant arms are formed, respectively, inthe resonant arms. And as shown in a sectional view taken along B-B′,detection electrodes 90A and 90D are provided on the outside walls ofeach of the through holes, and detection electrodes 90B and 90C areprovided on the inside walls of each of them. In the resonant arms, avoltage generated in the detection electrodes 90A and 90C, and a voltagegenerated in the detection electrodes 90B and 90D are reverse in phaseto each other.

[0229] As shown in this embodiment, a bending-vibration piece or aresonant arm can be bent by providing a pair of drive electrodes on theinside and the outside wall of each of two sides of a through holeformed in the bending-vibration piece or the resonant arm. The detectionside also goes in the same way.

[0230] In this invention, the above-mentioned main arm and at least apair of resonant arms can be provided at one side of the fixing piecepart and a resonant piece to resonate with the main arm can be providedat the other side of the fixing piece part. In this case, driveelectrodes are provided on a bending-vibration piece of the resonantpiece and detection electrodes are provided on the resonant arms. Bythis, it is possible to use a bending vibration of the bending-vibrationpiece of the resonant piece as a drive vibration and use a bendingvibration of the resonant arm as a detection vibration. Otherwise, driveelectrodes are provided on the resonant arms and detection electrodesare provided on the bending-vibration piece of the resonant piece. Bythis, it is possible to use a bending vibration of the resonant arm as adrive vibration and use a bending vibration of the bending-vibrationpiece of the resonant piece as a detection vibration.

[0231] In such a manner, furthermore, a second resonant arm can beprovided at the other side of the fixing piece part. FIG. 23 is aperspective view roughly showing a vibratory gyroscope 59G of thisembodiment.

[0232] In this vibrator 60G, a fixing piece part 12 is provided inside afixing member 90. At one side of the fixing piece part 12, a main arm101L and a pair of resonant arms 92A and 92B project from a projection94A. In the main arm 101L, bending-vibration pieces 91A and 91Bextending perpendicularly to the base part 3 are formed at an end sideof the base part 3. Drive electrodes 46A, 46B, 46C and 46D are providedon the bending-vibration pieces. Weights 93A and 93B are, respectively,provided at the top ends of the resonant arms.

[0233] In the bending-vibration pieces 91A and 91B, as shown in asectional view taken along A-A′, a voltage applying direction to thedrive electrodes 46A and 46C side and a voltage applying direction tothe driving electrodes 46B and 46D side are reverse in phase to eachother.

[0234] At the other side of the fixing piece part 12, a resonant arm 103and a pair of second resonant arms 97A and 97B project from a projection94B. In the resonant piece 103, bending-vibration pieces 95A and 95Bextending perpendicularly to a base part 98 are formed at an end side ofthe base part 98.

[0235] Weights 96A and 96B are, respectively, provided at the top endsof the resonant arms 97A and 97B. As shown in a sectional view takenalong B-B′, detection electrodes 49A, 49B, 49C and 49D are provided onthe resonant arms. A signal voltage generated in the detectionelectrodes 49A and 49C side and a signal voltage generated in thedetection electrodes 49B and 49D side are reverse in phase to eachother.

[0236] A second embodiment of the invention is described in more detailin the following.

[0237]FIG. 24 shows a construction of an example of a vibrator of theinvention. In the example shown in FIG. 24, a vibrator 108 extends inthe X-Y plane and is composed of a pair of tuning-fork vibration pieces109 a and 109 b, a pair of bending-vibration pieces 241 a and 241 b forjoining them in the X-Y plane, and a base part 3 for fixing thesebending-vibration pieces on an external fixing member 1 in the X-Yplane. The one pair of tuning-fork vibration pieces 109 a and 109 b arealmost in parallel with each other, and are joined with thebending-vibration pieces nearly perpendicularly to them. The base part 3is joined with the nearly middle part 25 between the bending-vibrationpieces 241 a and 241 b, and is almost in parallel with the tuning-forkvibration pieces 109 a and 109 b.

[0238] In the vibrator 108 having the above-mentioned composition of theinvention, when forces F1 and F2 different in direction from each otheract on both ends of the bending-vibration pieces 241 a and 241 b of thetuning-fork vibrator in parallel with the tuning-fork vibration pieces109 a and 109 b, namely, in the Y direction, a bending motion B having ajoint 26 where the base part 3 is joined with-the fixing part 1 as afulcrum takes place in the X-Y plane in the base part 3.

[0239] Although the tuning-fork vibration pieces, the bending-vibrationpieces, and the base part which form the vibrator 108 can be formed outof separate members, it is preferable to form them in one body from aviewpoint of manufacturability and the like in case of forming them outof a single crystal in particular. Although a material for them also isnot limited in particular, it is preferable to use a single crystal ofquartz, LiNbO₃, LiTaO₃, or Li(Nb, Ta)O3. Using these single crystalsmakes it possible to obtain a good detection sensitivity and reducedetection noises. And since they are insensitive to a temperaturechange, they are preferable for a sensor mounted in a car requiring athermal stability. Among the above-mentioned single crystals, sincesingle crystals of LiNbO₃ and LiTaO₃ have comparatively largeelectromechanical coupling coefficients, it is preferable to use asingle crystal of LiNbO₃ or LiTaO₃ rather than a quartz crystal.Comparing single crystals of LiNbO₃ and LiTaO₃ with each other, a singlecrystal of LiTaO₃ has a comparatively larger electromechanical couplingcoefficient than a single crystal of LiNbO₃, it is more preferable touse a single crystal of LiTaO₃ rather than a single crystal of LiNbO₃.

[0240] The vibrator 108 having the above-mentioned construction is usedmainly as a vibratory gyroscope. A case where a vibrator 1 is used asthe first invention of a vibratory gyroscope is considered in thefollowing. First, the tuning-fork vibration pieces are vibrated exactlyreversely in phase to each other in the X-Y plane by means of anunillustrated exciting means in a turning system having the Z axis asthe central axis. When a turning angular rate ω acts around the Z axisin this state, a Coriolis force makes forces F1 and F2 reverse indirection to each other act on the tuning-fork vibration pieces alongthe Y axis. As the result, moments M1 and M2 having the same directionact on both ends of the bending-vibration pieces. These moments M1 andM2 generate a bending vibration B in the X-Y plane in the base part 3. Aturning angular rate can be measured by detecting this bending vibrationB as deformation of the base part 3 by means of an unillustratedbending-vibration detecting means.

[0241] As described above, since the vibratory gyroscope of thisinvention converts a Coriolis force generated in the same X-Y plane asthe tuning-fork vibration pieces into a bending vibration of the basepart 3 and obtains a turning angular rate from the bending vibration, itcan detect a turning angular rate even when the vibrator is arrangedperpendicularly to the axis of turning (horizontally arranged).Accordingly, even in case of mounting the vibratory gyroscope of theinvention as an angular-speed sensor for the purpose of obtaining aturning angular rate of a car body for example, it can be shortened inheight for the mounting part.

[0242] Although the above-mentioned example vibrates the tuning-forkvibration pieces and the bending-vibration pieces in the X-Y plane andobtains a turning angular rate from a bending vibration of the base part3 in this state, it is also possible to replace vibration andmeasurement with each other. That is to say, as shown in FIG. 27, in astate of exciting a bending vibration B in the fixing part 3 by means ofan unillustrated exciting means, a Coriolis force generated on the basisof a turning angular rate makes forces F1 and F2 having the samedirection as each other act on the tuning-fork vibration pieces 109 aand 109 b along the Y axis. As the result, moments M1 and M2 having thedifferent directions from each other act on both ends of thebending-vibration pieces. In the same way, a turning angular rate can bemeasured by using an unillustrated vibration detecting means whichdetects vibration in the X-Y plane generated in the tuning-fork vibratorby these moments M1 and M2 and generates a signal according to thedetected vibration. This composition is the second invention of avibratory gyroscope of the invention.

[0243]FIG. 25 shows the construction of another example of a vibrator ofthe invention. In the example shown in FIG. 25, the same symbols aregiven to the same members as the members shown in FIG. 24 anddescription of them is omitted. The example shown in FIG. 25 isdifferent from the example shown in FIG. 24 in that projections 111 aand 111 b, respectively, projecting outer than the tuning-fork vibrationpieces 109 a and 109 b are provided at both ends of thebending-vibration pieces 241 a and 241 b forming the tuning-forkvibrator. In the example shown in FIG. 25, relation between theresonance frequency of vibration in the X-Y plane of the tuning-forkvibrator and the resonance frequency of a bending vibration of the basepart can be simply adjusted to a specified relation by reducing at leastone of the projections 111 a and 111 b in projection height.

[0244] Hereupon, when the resonance frequency of the tuning-forkvibrator and the resonance frequency of the base part 3 become close toeach other, the sensitivity becomes good but the response speed isdeteriorated, and when both of them become distant from each other, theresponse speed becomes good but the sensitivity is deteriorated.Therefore, relation between the resonance frequency of vibration in theX-Y plane of the tuning-fork vibrator and the resonance frequency of abending vibration of the base part 3 is adjusted to a specified relationin which both of the sensitivity and the response speed become good tosome degree.

[0245]FIG. 26 shows the construction of a further other example 98 of avibrator of the invention. In the example shown in FIG. 26 also, thesame symbols are given to the same members as the example shown in FIG.24 and description of them is omitted. The example shown in FIG. 26 isdifferent from the example shown in FIG. 24 in that while thetuning-fork vibration pieces 109 a and 109 b project from thebending-vibration pieces in a direction opposite to the base part 3 inrelation to the bending-vibration pieces in the example shown in FIG.24, the tuning-fork vibration pieces 109 a and 109 b project in the samedirection as the base part 3 in the example shown in FIG. 26. Avibratory gyroscope can be made more compact by forming it as shown inFIG. 26.

[0246] The variation examples of a vibrator shown in FIGS. 25 and 26also are used mainly in a vibratory gyroscope in the same way as thevibrator shown in FIG. 24, and act also in the same way as the exampleshown in FIG. 24. At that time, as an exciting means, abending-vibration detecting means, and a vibration detecting means whichare not illustrated, piezoelectric members of piezoceramic or the likecan be preferably used in the same way as used up to now. And in case ofusing a vibrator made of a piezoelectric single crystal as a vibrator,an exciting means, a bending-vibration detecting means and a vibrationdetecting means can be formed by providing electrodes at specifiedpositions. Furthermore, in a vibratory gyroscope using a vibrator havingthe construction shown in FIG. 24 or 25, since it is possible to form anexciting means and a bending-vibration detecting means or a vibrationdetecting means at positions distant from each other as well as toshorten the gyroscope in height by horizontally arranging it, it ispossible to further reduce a bad influence of an electromechanicalcoupling or the like between both of the exciting means and thedetecting means.

[0247] Moreover, in any example, a vibrator of the invention can excitea drive vibration and a detection vibration in the same plane, and canarrange both of the vibrations in the same direction. Therefore, even incase of forming a vibrator of the invention out of a single crystal ofquartz, LiNbO₃, LiTaO₃ or the like, if a frequency difference betweenthe resonance frequency of a drive vibration and the resonance frequencyof a detection vibration is adjusted to a certain frequency differenceat which the detection sensitivity becomes the best, the relationbetween them is kept and is not influenced by anisotropy of the singlecrystal even when temperature varies. Therefore, a good detectionsensitivity, a small detection noise, and a high thermal stability whichare features of a single crystal known from the past can be displayed tothe maximum.

[0248] A third embodiment of the invention is described in thefollowing.

[0249] In an example shown in FIG. 28, a vibrator is provided with afixing piece part 115 both ends of which are fixed on fixing members114, and a main arm 121 composed of a tuning-fork vibrator 118 formed byjoining a pair of tuning-fork vibration pieces 119 a and 119 b withbending-vibration pieces 241 a and 241 b in a specified plane and a basepart 3 for fixing this tuning-fork vibrator on the fixing piece part 115in a plane. And the vibrator is provided with a resonant piece 123provided on the fixing piece part at a position which corresponds to andis opposite to the base part 3. In this example, as the resonant piece123, a resonant piece which has the same shape and the same compositionas the main arm 121 is provided on the fixing piece part at a positionline-symmetrical to the main arm in relation to the fixing piece part.In this case, a vibration frequency of the main arm and the resonancefrequency of the resonant piece can be made equal to each other.Hereupon, 122 is a joint at the resonant piece side, 120 a and 120 brepresent driving electrodes, 117 represents a detecting electrode, andthey are necessary for forming the whole vibratory gyroscope out of asingle crystal.

[0250] Although the fixing piece part, the main arm, and the resonantpiece can be formed out of separate members, it is preferable to formthem in one body from a viewpoint of ease of manufacture or the like incase of forming them out of a single crystal in particular. Although amaterial for them is not limited in particular, as described above, itis preferable to use a single crystal of quartz, LiNbO₃, LiTaO₃, orLi(Nb, Ta)O₃.

[0251] In a vibrator of the invention having the above-mentionedconstruction, when forces F1 and F2 different in direction from eachother act on both ends of the bending-vibration pieces of thetuning-fork vibrator 118 in parallel with the tuning-fork vibrationpieces 119 a and 119 b, namely, in the Y direction, a bending vibrationB1 having a joint 116 where the base part 3 is joined with the fixingpiece part 115 as a fulcrum is generated in the base part 3 in the X-Yplane. At the same time, a bending vibration B2 in the same directionwith the joint 116 as a fulcrum is generated by this bending vibrationB1 of the base part 3. Accordingly, a drive vibration of the vibrator isas shown in FIG. 29(a), and a bending vibration for detection of thevibrator at this time is as shown in FIG. 29(b).

[0252] The vibrator having the above-mentioned construction is usedmainly as a vibratory gyroscope. A case where a vibrator is used as thefirst invention of a vibratory gyroscope is thought with reference toFIG. 28 in the following. First, the tuning-fork vibration pieces arevibrated completely reverse in phase to each other in the X-Y plane bymeans of drive electrodes 120 a and 120 b as an exciting means in aturning system having the Z axis as the central axis. When a turningangular rate ω acts around the Z axis in this state, a Coriolis forcemakes forces F1 and F2 along the Y axis in reverse directions to eachother act on the tuning-fork vibration pieces. As the result, moments M1and M2 in the same direction act on both ends of the bending-vibrationpieces of the tuning-fork vibrator 118. Thanks to these moments M1 andM2, a bending vibration B1 in the X-Y plane is generated in the basepart 3 of the main arm, and a bending vibration B2 in the X-Y plane isgenerated also in the resonant piece 123. A turning angular rate ω canbe measured by detecting this bending vibration B2 by means of adetecting electrode 117 as a bending-vibration detecting means providedon the resonant piece.

[0253] As described above, since a vibratory gyroscope of the inventionconverts a Coriolis force generated in the same X-Y plane as thetuning-fork vibration pieces into a bending vibration of the base part 3and the resonant piece 123 and obtains a turning angular rate from thebending vibration, it can detect a turning angular rate even when thevibrator is disposed perpendicularly to the axis of turning(horizontally disposed). Accordingly, even in case of mounting thevibratory gyroscope of the invention as an angular-speed sensor for thepurpose of obtaining a turning angular rate of a car body for example,it can be shortened in height for the mounting part. And in thisexample, since the vibratory gyroscope is provided with the main arm andthe resonant piece at positions symmetrical to each other in relation tothe fixing piece part 115, a driving means provided on the main arm anda detecting means provided on the resonant piece can be made distantfrom each other, and a bad influence such as an electromechanicalcoupling or the like can be prevented.

[0254] FIGS. 30 to 33 show construction of other examples of theinvention. In FIGS. 30 to 33, the same symbols are given to the samemembers as the members shown in FIG. 28 and description of them isomitted. In the example shown in FIG. 30, a resonant piece 123 iscomposed of a rectangular resonant piece 124 extending from andperpendicularly to a fixing piece part 115. In this case, the vibratorcan be simplified in construction. In the example shown in FIG. 31, theresonant piece shown in FIG. 30 is shortened and an expanded part 126 isprovided at the top end of a resonant piece 125. Thanks to this, thisexample can make the resonant piece lower in projection height from afixing piece part and can make the vibrator more compact, and moreovercan make the resonance frequency of the resonant piece closer to avibration frequency of the main arm in comparison with the example shownin FIG. 30. Differently from the example shown in FIG. 28, in an exampleshown in FIG. 32 a pair of tuning-fork vibration pieces 119 a and 119 bis projected in the same direction as the base part 3 from thebending-vibration pieces 241 a and 241 b. Thanks to this, the gyroscopecan be made more compact in comparison with the example shown in FIG.28.

[0255] An example shown in FIG. 33 forms the second invention of avibratory gyroscope of the invention. That is to say, although thevibratory gyroscope using the vibrator of the invention shown in FIG. 28vibrates the tuning-fork vibrator 118 in the X-Y plane and obtains aturning angular rate from the bending vibration of the resonant piece 9in that state, this example replaces vibration and measurement with eachother in composition. In the example shown in FIG. 33, in a state wherea bending vibration BI is generated in a base part 3 by a driveelectrode 250 as an exciting means and a bending vibration B2 isgenerated in a base part 125 of a resonant piece 123, a Coriolis forcegenerated on the basis of a turning angular rate makes forces F1 and F2along the Y axis in the same direction act on the tuning-fork vibrationpieces 127 a and 127 b. As the result, moments M1 and M2 in differentdirections from each other act on both ends of the tuning-fork vibrator128. A turning angular rate can be measured by using detectingelectrodes 117 a and 117 b as a vibration detecting means for detectingvibration in the X-Y plane generated in the tuning-fork vibrator 128 bythese moments M1 and M2 and generating a signal according to thedetected vibration. It is a matter of course that a turning angular ratecan be also measured by means of only one of the detecting electrodes117 a and 117 b. In this example, 126 represents a joint.

[0256] In variation examples shown in FIGS. 30 to 33, on the assumptionthat the whole of a vibrator is formed out of a single crystal ofquartz, LiNbO₃ or LiTaO₃, although a driving electrode is provided as anexciting means and a detecting electrode is provided as abending-vibration detecting means, in case of forming a vibrator out ofanother material used for a vibratory gyroscope up to now, apiezoelectric material of piezoceramic or the like can be preferablyused as an exciting means, a bending-vibration detecting means and avibration detecting means in the same way as used from the past.

[0257]FIG. 34 shows the construction of a further other example of avibrator of the invention. In the example shown in FIG. 34, the samesymbols are given to the same members as the members shown in FIG. 28,and description of them is omitted. The example shown in FIG. 34 isdifferent from the example shown in FIG. 28 in that projections 127 aand 127 b, respectively, extending outer than the tuning-fork vibrationpieces 119 a and 119 b are provided at both ends of thebending-vibration pieces 241 a and 241 b forming the tuning-forkvibrator 118. In the example shown in FIG. 34, relation between theresonance frequency of vibration in the X-Y plane of the tuning-forkvibrator and the resonance frequency of a bending vibration of a basepart and a resonant piece can be simply adjusted to a specified relationby reducing at least one of the projections in projection height.

[0258] Hereupon, when the resonance frequency of the tuning-forkvibrator and the resonance frequency of the base part and the resonantpiece become close to each other, the sensitivity becomes good but theresponse speed is deteriorated, and when both of them become distantfrom each other, the response speed becomes good but the sensitivity isdeteriorated. Therefore, relation between the resonance frequency ofvibration of the tuning-fork vibrator and the resonance frequency of abending vibration of the base part and the resonant piece is adjusted toa specified relation in which both of the sensitivity and the responsespeed become good to some degree.

[0259] A fourth embodiment of the invention is described in thefollowing.

[0260] FIGS. 35 to 38 illustrate mainly the shapes of vibrators ofvibratory gyroscopes of the invention.

[0261]FIG. 35 is a perspective view showing a vibrator 98 of thisembodiment. Since this is almost the same as the vibrator 98 shown inFIG. 26 in this specification, description of the duplicated parts isomitted and the above-mentioned description is quoted. In FIG. 35, 111aand 111 b represent projections.

[0262]FIG. 36 is a front view showing another vibrator 101E, and sincethis is almost the same as the vibrator shown in FIG. 11 in thisspecification, description of the duplicated parts is omitted and theabove-mentioned description is quoted.

[0263] A vibrator as described above can be applied to a vibrator calleda H-shaped vibrator. For example, a vibrator provided with a fixingpiece part both ends of which are fixed, a base part provided at oneside of the fixing piece part, at least one bending-vibration pieceextending from the base part in a direction crossing the longitudinaldirection of the base part, and a resonant piece provided at the otherside of the fixing piece part, wherein the fixing piece part, the basepart, the bending-vibration piece, and the resonant piece are formed soas to extend substantially in a specified plane can be manufactured.

[0264]FIG. 37 is a front view showing a vibrator 10 of this embodiment.Since this is almost the same as the vibrator shown in FIG. 6 in thisspecification, description of the duplicated parts is omitted.

[0265]FIG. 38 is a front view showing a three-forked tuning-forkvibrator 131. The vibrator 131 is provided with a base part 135 to befixed on an external fixing member and three vibration pieces 132, 133and 134 of a three-forked type projecting from the base part. Thevibration pieces 132 and 134 at both sides comprise main body parts 132a and 134 a projecting long and slenderly from the base part 135, andweight parts 132 b and 134 b respectively extending from andperpendicularly to the main body parts. Detecting electrodes 136 and 137are formed, respectively, on the vibration pieces 132 and 134. A pair ofdriving electrodes 138A and 138B are formed on the middle vibrationpiece 133.

[0266] In any of the examples shown in FIGS. 35 to 38, since a vibratorygyroscope can be formed in a state where a vibrator is horizontallydisposed, it is possible to shorten the gyroscope in height. And since aspecified single crystal is used as a vibrator so that the vibrator canbe made by means of etching, grinding or the like, the vibrator can besimply manufactured and the gyroscope can be produced at a low cost.Moreover, as shown in FIG. 37, in case of providing a vibration pieceand a resonant piece on a fixing piece part symmetrically to each otherin relation to the fixing piece part, since a driving means provided onthe vibration piece and a detecting means provided on the resonant piececan be made distant from each other, it is possible to prevent a badinfluence caused by an electromechanical coupling or the like betweenboth of them.

[0267] A method for detecting a turning angular rate in a vibratorygyroscope provided with a horizontal-arrangement vibrator composed of apiezoelectric single crystal having the above-mentioned composition isdescribed in the following. First, in a method for detecting a turningangular rate in a former gyroscope, it is known that a leakage signaldue to an unnecessary vibration which is generated by an influence of adrive signal and is caused by an insufficient machining accuracy or thelike is contained in an output signal detected by a detecting means.Since when this leakage signal is large it is difficult to detect agyroscopic signal caused by a Coriolis force in an output signal, aformer method of obtaining a turning angular rate from the amplitude ofan output signal has removed the influence of a leakage signal by meansof taking a differential output from detecting means provided at twopositions.

[0268] Such an influence of a leakage signal becomes hardly a problem ina vibratory gyroscope using a vibrator which is a vertical-arrangementtuning-piece vibrator as disclosed in the Japanese patent publicationTokkohei No. 4-14734 described in the prior art section, furthermore isformed out of a constant-elasticity metal, and is high in detectionsensitivity. Moreover, as disclosed in the Japanese patent publicationTokkohei No. 4-14734, in case of detecting a turning angular rate on thebasis of variation of a phase difference between a drive signal anddetection signal, since variation of a phase difference is littleinfluenced by a leakage signal, the leakage signal becomes hardly aproblem.

[0269] In case of horizontally disposing a vibrator in the same manneras the present invention, since a gyroscopic signal caused by a Coriolisforce is made small due to its composition and the detection sensitivityis low, it is thought in general that the above-mentioned method ofdetection by a phase difference cannot be applied as it is. As theresult of studying this point in various ways, the inventors have foundthat a turning angular rate can be accurately detected on the basis of aphase difference between a reference signal and an output signal even ina range where a leakage signal is large and a gyroscopic signal issmall, by using a piezoelectric single crystal. Additionally, theinventors have found that an output signal in a range where a leakagesignal is fairly larger and a gyroscopic signal is fairly smaller thanthose in a range which is thought to be suitable for measurement ingeneral is better in linearity of a phase difference to a turningangular rate and can be measured in higher accuracy.

[0270]FIG. 39 is a block diagram showing an example of a phasedifference detecting means in a vibratory gyroscope of the invention. InFIG. 39, it is assumed that an electric signal used for generating adrive vibration is a reference signal and an electric signal taken outby a detecting means from a vibration which has a vibration modedifferent from the drive vibration and is generated with the drivevibration is an output signal.

[0271] Concretely, in the example shown in FIG. 35, an electric signalsupplied to an unillustrated driving electrode provided on thetuning-fork vibration piece 109 a or 109 b is a reference signal, and anelectric signal detected by an unillustrated detecting electrodeprovided on the base part is an output signal. And in the example shownin FIG. 36, an electric signal supplied to the exciting means 5A and 5Bis a reference signal, and an electric signal detected by the detectingmeans 6A, 6B, 6C and 6D is an output signal. Furthermore, in the exampleshown in FIG. 37, an electric signal supplied to the exciting means 5Aand 5B is a reference signal, and an electric signal detected by thedetecting means 6A, 6B, 6C and 6D is an output signal. Still further, inthe example shown in FIG. 38, an electric signal supplied to theelectrodes 136 and 137 is a reference signal, and an electric signaldetected by the electrodes 138A and 138B is an output signal.

[0272] Although in the above-mentioned examples an electric signal usedfor generating a drive vibration is used as a reference signal, anelectric signal obtained by resonating the drive vibration itself can beused as a reference signal.

[0273] In a phase detecting means 139 shown in FIG. 39, an output signalis amplified by an alternating-current amplifier 140 and then issupplied to a phase different detecting circuit 141. A reference signalis preprocessed for waveform-shaping or the like by a reference signalpreprocessing circuit 142, and then is supplied to a phase differentdetecting circuit 141 in the same way. The phase difference detectingcircuit 141 detects a phase difference between a preprocessed referencesignal and an output signal which have been supplied. The detected phasedifference is supplied to a low-pass filter 143 and a direct-currentamplifier 144 to be a direct-current signal according to the phasedifference. A direct-current signal obtained by the above-mentionedphase difference detecting means 139 is supplied to a turning angularrate detecting circuit 145. The turning angular rate detecting circuitobtains a turning angular rate on the basis of a predetermined relationbetween the magnitude of a direct current and a turning angular rate.Since the above-mentioned circuit cannot directly obtain a phasedifference between an output signal and a reference signal as anumerical value, it obtains a turning angular rate from the magnitude ofa direct-current signal according to a phase difference, but it ispossible also to directly obtain a phase difference as a numerical valueand then obtain a turning angular rate on the basis of a predeterminedrelation between a phase difference and a turning angular rate.

[0274] Relation between a leakage signal and a gyroscopic signal whichform an output signal is described in the following. The inventors haveobtained a phase difference between a reference signal and an outputsignal and examined the relationship between a variation of the obtainedphase difference and a turning angular rate in a vibratory gyroscopehaving a vibrator which has the construction shown in FIG. 38 and iscomposed of a single crystal of LiTaO₃. The result is shown in FIGS. 40to 42. FIG. 40 shows the relation in case that the ratio of a gyroscopicsignal to a leakage signal is 1:100 at a turning angular rate of100°/second, FIG. 41 shows the relation in case that the ratio of agyroscopic signal to a leakage signal is 1:7 at a turning angular rateof 100°/second, and FIG. 42 shows the relation in case that the ratio ofa gyroscopic signal to a leakage signal is 5:1 at a turning angular rateof 100°/second. Hereupon, the ratio of the amplitude of a signal whichis excited by a Coriolis force and is outputted at the time of turningat a turning angular rate of 100°/second in an output signal to theamplitude of a signal which is outputted at the time of turning at aturning angular rate of zero in an output signal is referred to as theratio of a gyroscopic signal to a leakage signal at a turning angularrate of 100°/second. A vector diagram shown in each of the figures showsthe relationship among an output signal, a gyroscopic signal and aleakage signal under each condition in case of taking a phase angle in aturning direction with the origin of a vector as the center, and takingthe magnitude of a signal in a radial direction. And each of the figuresshows a case where a leakage signal and a reference signal are the samein phase, and represents a phase difference between a leakage signal anda output signal as a phase difference between a reference signal and anoutput signal. Hereupon, in case that there is a certain phasedifference between a leakage signal and a reference signal, variation ofa phase difference is as illustrated.

[0275] From the result shown in FIG. 40, it has been found that in avibratory gyroscope using a horizontal-arrangement vibrator also, incase of using a piezoelectric single crystal, it is possible to detect aminute phase difference of such a low level as shown in FIG. 40 andobtain a high linearity between a phase difference and a turning angularrate in such a case. From the result shown in FIG. 41 also, it has beenfound that it is possible to obtain a high linearity although it is notso good as shown in FIG. 40. On the other hand, from the result shown inFIG. 42, it has been found that the linearity between a phase differenceand a turning angular rate cannot be kept, the usable range is limitedto a turning angular rate of ±50°/second or so, and it is difficult todetect a phase difference at a turning angular rate in a range of 70° to100°/second. The above-mentioned results are collected as relationbetween the linearity of a phase difference to a turning angular rateand the ratio of a gyroscopic signal to a leakage signal in FIG. 43.

[0276] Since it is generally thought to need a linearity of ±1%, whenobtaining a range satisfying the above-mentioned conditions from theresult shown in FIG. 43, it has been found that the above-mentionedrelation of linearity can be obtained in a range where a leakage signalis so large that the ratio of a gyroscopic signal to a leakage signal is1:7 or more. However, too large a leakage signal exceeds the detectionlimit of a vibrator even if it uses a piezoelectric single crystal.Therefore, the upper limit of a leakage signal is determined accordingto the sensitivity of a vibratory gyroscope.

[0277] In the present invention, as described above, in a range wherethe ratio of a leakage signal to a gyroscopic signal is larger than aspecified ratio at a specified turning angular rate, the detectionsensitivity is low but the linearity of a phase difference to a turningangular rate is good, and it is possible to improve the signal-to-noiseratio in relation to noises caused by external factors in comparisonwith the prior art by forming a horizontal-arrangement vibrator out of apiezoelectric single crystal good in mechanical quality. Since theinvention can cope with a large leakage signal and does not need amanufacturing apparatus of high machining accuracy for manufacturing avibrator, the invention can greatly reduce the manufacturing cost andcan dispense with an adjusting process by reprocessing performedaccording to circumstances up to now. And the invention dispenses with acircuit and the like for removing a leakage signal provided according tocircumstances up to now.

[0278] A fifth embodiment of the invention is described in thefollowing.

[0279] The inventors made a vibrator 147 shown in FIG. 44, and performedan experiment of detecting a turning angular rate using the vibrator.Hereupon, the vibrator is formed out of a piezoelectric single crystal,and is provided with a fixing part 2 fixed on an external constructionand a pair of long and narrow tuning-fork vibration arms 148A and 148Bprojecting from the fixing part 2. A gap 149 is formed between the pairof vibration arms. In a coordinate system shown in FIG. 44, main faces150A and 150B of the vibrator are directed to the Y-axis direction, andside faces 151A and 151B are directed to the X-axis direction.

[0280] The vibration arms of the vibrator are vibrated in the Xdirection as shown by arrows C and D. When the vibrator is turned aroundthe Z axis as shown by ω in this state, the vibration arms arerespectively vibrated in the Y-axis direction as shown by arrows A andB. A turning angular rate is computed by detecting this vibration.Theoretically, it is possible to first vibrate the vibration arms asshown in arrows A and B, turn the vibrator around the Z axis in thisstate, vibrate the vibration arms as shown by arrow C and D, and detectthis vibration.

[0281] In such a vibrator 147, the vibration arms 148A and B need to bevibrated in the Y-axis direction, or vibrations of the vibration arms inthe Y-axis direction need to be converted to electric signals. As forsuch an exciting method, a method shown in FIG. 45 is disclosed in“Three-Forked Tuning-Fork Resonator Aiming at a Horizontal-ArrangementVibratory Gyroscope Sensor” in pp. 1071 to 1072 of “Japan Society ofAcoustics Engineers '96 Spring Convention Proceedings II issued in March1996 by Japan Society of Acoustics Engineers”. FIG. 45(a) is a plan viewof the vibration arm 148A or 148B, and FIG. 45(b) is a front view of it.

[0282] Electrodes 152A and 152B are formed, respectively, on the mainfaces 150A and 150B of each vibration arm, and electrodes 153A and 153Bare also formed, respectively, on the side faces 151A and 151B. Thedirection of polarization of a piezoelectric single crystal forming thevibration arms is assumed as a direction shown by arrow E. It is assumedthat the opposite electrodes 152A and 152B are the same in phase, andthe opposite electrodes 153A and 153B are the same in phase. At acertain moment the opposite electrodes 152A and 152B become negative,and the opposite electrodes 153A and 153B become positive.

[0283] At this time, in the upper half part of the vibration arm in FIG.45(a), an electric field is generated slantly upward as shown by arrowsF and G. A component of this electric field in the Y-axis direction isin the +Y direction, which coincides with the direction of polarizationE of the piezoelectric single crystal. Therefore, the vibration arm iscontracted as shown by arrow K in FIG. 45(b).

[0284] On the other hand, in the lower half part of the vibration arm inFIG. 45(a), an electric field is generated islantly downward as shown byarrows H and I. A component of this electric field in the Y-axisdirection is in the −Y direction, which is reverse to the direction ofpolarization E of the piezoelectric single crystal. Therefore, thevibration arm is extended as shown by arrow J in FIG. 45(b). As theresult, the vibration arm is bent as shown arrow A(B).

[0285] As a result of a detailed examination of the vibrator performedby the inventors, the following problem has been found. That is to say,although it is preferable to make larger the magnitude of displacementin a bending vibration generated by an applied voltage, it has beenfound that this has a limit. And displacements of bending vibrations inthe respective parts inside the vibration arm are ununiform inmagnitude, and internal strain or internal stress is generated insidethe vibration arm at the time of vibration. Due to this, the magnitudeof an applied voltage and the magnitude of displacement of a bendingvibration of the vibration arm do not have necessarily a linearrelation, and the vibrators have large variations in production withregard to the relation between the magnitude of an applied voltage andthe magnitude of displacement of a bending vibration of the vibrationarm.

[0286] This is thought to be caused by ununiformity in the internalelectric field of the vibration arm in FIG. 45(a). For example, anelectric field is applied as shown in arrow F or H in a domain 154 closeto a corner, and in these domains, the electrodes 153A and 153B and theelectrodes 152A and 152B are, respectively, close to each other, and soa strong electric field is applied to the piezoelectric single crystalat each of these domains. On the other hand, an electric field isapplied as shown in arrow G or I in a domain 155 distant from a corner,and an applied electric field is weak in such a domain 155 distant froma corner. In this way, it is thought that an electric field greatlyvaries with the position in the piezoelectric single crystal forming avibrator and this variation appears as internal stress and internalstrain.

[0287]FIG. 46 is a perspective view showing a vibratory gyroscope of anembodiment of the invention, FIG. 47(a) is a plan view of a plane-normalvibration arm 158A in FIG. 46, FIG. 47(b) is a front view of theplane-normal vibration arm 158A taken in the direction of the X axis,and FIG. 48 is a schematic view for explaining operation of aplane-parallel vibration 154.

[0288] A vibrator 156 is provided with a fixing part 157 fixed on anexternal fixing member, and a pair of tuning-fork vibration arms 154 and158A (158B or 158C) projecting from the fixing part. The whole vibratoris composed of a joined member obtained by joining two plate-shapedmembers 159A and 159B to each other. The direction of polarization(shown by arrow 165) of the plate-shaped member 159A and the directionof polarization (shown by arrow 166) of the plate-shaped member 159B areexactly opposite to each other, and are perpendicular to one main face161A and the other main face 161B.

[0289] One electrode 163A and the other electrode 163B are respectivelyformed on the main faces of the plane-normal vibration arm 158A. Noelectrode is formed on the respective side faces 162A and 162B of thevibration arm 158A. And electrodes 155A and 155B are formed on one mainface 161A of the plane-parallel vibration arm 154, and electrodes 155Cand 155D are formed on the other main face 161B of it, and no electrodeis formed on the respective side faces of the vibration arm 154. A gap160 is provided between the vibration arms 154 and 158A.

[0290] In a coordinate system shown in FIG. 46, the main faces of thevibrator are directed to the Y-axis direction, and the side faces aredirected to the X-axis direction.

[0291] The plane-normal vibration arm 158A is vibrated by applying analternating voltage to a pair of electrodes 163A and 163B. In this case,at a certain moment one electrode 163A becomes positive and the otherelectrode 163B becomes negative as shown in FIG. 47(a). At this moment avoltage is applied from the electrode 163A to the electrode 163B.

[0292] At this time the direction of an electric field and the directionof polarization 165 become exactly opposite to each other inside theplate-shaped member 159A. As the result, the plate-shaped member 159A isexpanded as shown by arrow J as shown in FIG. 47(b). On the other hand,the direction of an electric field and the direction of polarization 166become the same as each other inside the plate-shaped member 159B. Asthe result, the plate-shaped member 159B is contracted as shown by arrowK as shown in FIG. 47(b). By this, the whole vibration arm can bebending-vibrated as shown by arrow B. At this time the plane-parallelvibration arm 154 is resonated as shown by arrow A by setting theresonance frequencies of the vibration arms as a specified value.

[0293] When the vibrator is turned around the Z axis as shown by ω inthis state, the vibration arms 154 and 158A are respectively vibrated inthe X-axis direction as shown by arrows C and D. A turning angular rateis computed by detecting a plane-parallel vibration as shown by arrow Cby means of the plane-parallel vibration arm 154.

[0294] Concretely, as shown in FIG. 48, the electrodes 155A and 155C areconnected to a voltage detecting apparatus 168, and the electrodes 155Band 155C are grounded. When a bending vibration as shown by arrow C isapplied to the plane-parallel vibration arm 154 in this state, anelectric field as shown by arrow 167 is excited, and according to this,electromotive forces are generated, respectively, between the electrodes155A and 155B, and between the electrodes 155C and 155D. This voltagesignal is detected and a turning angular rate is detected from thisvalue.

[0295] The plane-normal vibration arm 154 of the vibration can bevibrated in the X direction as shown by arrow C. In order to do so, theelectrodes 155A and 155C are connected to a specifiedalternating-current power source, and an electric field 167 is appliedbetween the electrodes 155A and 155B, and between the electrodes 155Cand 155D. In this case, in FIG. 48 the direction of an electric fieldand the direction of polarization become reverse to each other indomains close to the electrodes 155A and 155C in the plane-parallelvibration arm 154, while the direction of an electric field and thedirection of polarization become nearly equal to each other in domainsclose to the electrodes 155B and 155D. Thanks to this, theplane-parallel vibration arm is vibrated as shown by arrow C. On theother hand, the plane-normal vibration arm is resonated as shown byarrow D.

[0296] When the vibrator is turned around the Z axis as shown by ω inthis state, the vibration arms 154 and 158A are respectively vibrated inthe Y-axis direction as shown by arrows A and B. An electromotive forceis generated between the electrodes 163A and 163B by this vibration ofthe vibration arm 158A. At this time the electrodes 163A and 163B areconnected to a specified voltage detecting apparatus 168. A turningangular rate is computed by measuring this voltage.

[0297] FIGS. 49(a) and 50(a) are, respectively, plan views of vibrationarms of vibrators of other embodiments of the invention, and FIGS. 49(b)and 50(b) are, respectively, front views of the vibration arms of FIGS.49(a) and 50(a) taken in the direction of the X axis. The same symbolsare given to the same components as the components shown in FIGS. 47(a)and 47(b), and description of them is omitted.

[0298] In FIGS. 49(a) and 49(b), the vibration arm 158B is composed of ajoined member obtained by joining a pair of plate-shaped members 169Aand 169B to each other. The direction of polarization (shown by arrow180) of the plate-shaped member 169A and the direction of polarization(shown by arrow 181) of the plate-shaped member 169B are exactlyopposite to each other, and are perpendicular to one main face 161A andthe other main face

[0299] An alternating voltage is applied to a pair of electrodes. Inthis case, at a certain moment one electrode 163A becomes negative andthe other electrode 163B becomes positive as shown in FIG. 49(a). Atthis moment a voltage is applied from the electrode 163B to theelectrode 163A.

[0300] At this time the direction of an electric field and the directionof polarization become exactly opposite to each other inside theplate-shaped member 169A. As the result, the plate-shaped member 169A isexpanded as shown by arrow J as shown in FIG. 49(b). On the other hand,the direction of an electric field and the direction of polarizationbecome equal to each other inside the plate-shaped member 169B. As theresult, the plate-shaped member 169B is contracted as shown by arrow Kas shown in FIG. 49(b). Thanks to this, the whole vibration arm 158B isbending-vibrated as shown by arrows A and B.

[0301] In FIGS. 50(a) and 50(b), the vibration arm 158C is composed of ajoined member obtained by joining a pair of plate-shaped members 251Aand 251B to each other. The direction of polarization (shown by arrow165) of the plate-shaped member 251A is perpendicular to the main faces.The direction of polarization (shown by arrow 172) of the plate-shapedmember 251B is in parallel with the main faces. In such a case also, thevibration arm of the invention can be moved perpendicularly to the mainfaces.

[0302] That is to say, an alternating voltage is applied to a pair ofelectrodes. In this case, at a certain moment one electrode 163A becomespositive and the other electrode 163B becomes negative as shown in FIG.50(a). At this moment a voltage is applied from the electrode 163A tothe electrode 163B.

[0303] At this time the direction of an electric field and the directionof polarization become exactly opposite to each other inside theplate-shaped member 251A. As the result, the plate-shaped member 251A isexpanded as shown by arrow J as shown in FIG. 50(b). On the other hand,contraction and expansion in such a direction are a little inside theplate-shaped member 251B. However, the whole vibration arm 158C isbending-vibrated as shown by arrows A and B due to expansion andcontraction of the plate-shaped member 251A.

[0304] FIGS. 51 to 53 are, respectively, perspective views showingthree-forked tuning-fork vibrators of vibratory gyroscopes of theinvention. In FIGS. 51 to 53, description of the composition alreadydescribed in FIG. 47 is omitted.

[0305] A vibrator 170 of a vibratory gyroscope shown in FIG. 51 isprovided with a fixing part 157 fixed on an external fixing member, andthree tuning-fork vibration arms 171A, 172 and 171B projecting from thefixing part. The whole vibrator is composed of a joined member obtainedby joining two plate-shaped members 159A and 159B to each other. Thedirection of polarization of the plate-shaped member 159A and thedirection of polarization of the plate-shaped member 159B are exactlyopposite to each other, and are perpendicular to the main faces 161A and161B.

[0306] One electrode 163A is formed on one main face 161A of each of theplane-normal vibration arms 171A and 171B, and the other electrode 163Bis formed on the other main face 161B (163B is not illustrated; see FIG.47). In the plane-parallel vibration arm 172, the above-mentionedelectrodes 155A and 155B are formed on one main face, and the oppositeelectrodes 155C and 155D are formed on the other main face (155C and155D are not illustrated; see FIG. 48).

[0307] Gaps 160 are formed, respectively, between the vibration arms171A and 172 and between the vibration arms 172 and 171B. In each ofcoordinate systems shown in FIGS. 51 to 53, the main face of thevibrator is directed to the Y-axis direction, and the side face isdirected to the X-axis direction.

[0308] In FIG. 51, for example, the middle plane-parallel vibration arm172 is excited as shown by arrow Q, and the vibration arms 171A and 171Bat both sides are resonated, respectively, as shown by arrows P and R.When the vibrator 170 is turned around the Z axis as shown by arrow ω,the vibration arms 171A and 171B are vibrated in the Y-axis direction,respectively, as shown by arrows S and U. At the same time, the middlevibration arm 172 is vibrated in the Y-axis direction as shown by arrowT. According to the invention, these vibrations of the vibration arms171A and 171B generate electromotive forces among the electrodes. Aturning angular rate is detected by measuring this voltage.

[0309] A vibrator 173 shown in FIG. 52 is provided with plane-parallelvibration arms 172A and 172B at both sides and a plane-normal vibrationarm 171 in the middle. The plane-parallel vibration arms at both sidesare, respectively, driven in the X-axis direction as shown by arrows Pand R, and the middle plane-normal vibration arm is resonated as shownby arrow Q. After this, the operation is the same as the case of FIG.51.

[0310] And according to the invention, it is possible to drive themiddle plane-normal vibration arm as shown by arrow T and resonate theplane-parallel vibration arms at both sides, respectively, as shown byarrows S and U. When the vibrator is turned around the Z axis as shownby ω in this state, the vibration arms 172A and 172B are vibrated in theX-axis direction as shown by arrows P and R. At the same time as this,the plane-normal vibration arm 171 is vibrated in the X-axis directionas shown by arrow Q. The plane-parallel vibrations of the vibration arms172A and 172B generate electromotive forces between the electrodes 155Aand 155B, and between the electrodes 155C and 155D. A turning angularrate is detected by measuring this voltage.

[0311] In a three-forked tuning-fork vibrator 174 of a vibratorygyroscope shown in FIG. 53, a plane-parallel vibration arm 172 isprovided at one end part and a plane-normal vibration arm 171 is provideat the other end part. The plane-parallel vibration arm 172 is driven asshown by arrow N, and the plane-normal vibration arm 171 is resonated asshown by arrow V. When the vibrator 174 is turned around the Z axis asshown by arrow ω in this state, the vibration arms 172 and 171 arevibrated in the opposite directions as shown by arrows W and Ω.According to the invention, an electromotive force is generated betweenthe electrodes by vibration of the vibration arm 171. A turning angularrate is detected by measuring this voltage. The middle arm 175 is notvibrated.

[0312] And according to the invention, it is possible to drive theplane-normal vibration arm 171 as shown by arrow W and resonate theplane-parallel vibration arm 172 as shown by arrow Ω. When the vibratoris turned around the Z axis as shown by ω in this state, the vibrationarms 171 and 172 are vibrated in the X-axis direction as shown by arrowsV and N. Hereupon, a turning angular rate is detected by measuring avoltage generated by vibration of the plane-parallel vibration arm 172.

[0313] Next, a preferred method for manufacturing a vibrator or avibration arm of the invention is described. In a preferred embodimentof the invention, plural plate-shaped members each of which is composedof a piezoelectric single crystal are prepared. In this case, therespective plate-shaped members are made different from one another indirection of the axis of polarization. A base member provided withplural plate-shaped members which are different from one another indirection of the axis of polarization is manufactured by joining theseplate-shaped members with one another. Then a vibrator is formed bycutting this base member.

[0314] The plural plate-shaped members can be adhered to one another byadhesives. And a laminated member is obtained by laminating the pluralplate-shaped members and then the laminated member can be internallyadhered by a heat treatment. It can be thought also to form pluraldomains which are different from one another in direction of the axis ofpolarization inside a single plate-shaped member by heat-treating thesingle plate-shaped member.

[0315] According to the above-mentioned manufacturing method, a vibratorcapable of performing a bending vibration in directions crossing themain faces of the vibrator can be manufactured by forming electrodes onone main face and the other main face of the vibrator. That is to say,electrodes for making the vibrator perform a bending vibration do nothave to be formed on the side faces of the vibrator, concretely, on thecut-off faces. Accordingly, it is possible to dispense with a process offorming the electrodes on the side faces of the vibrator, and thanks tothis, the manufacturing cost can be remarkably reduced and variations inperformance generated in production can be also reduced.

[0316] In the above-mentioned manufacturing method, it is particularlypreferable to form electrodes having a specified plane shape on one mainface and the other main face of a base member and then form a vibratorby cutting the base member. By doing so, electrodes for plural vibratorscan be formed by one electrode forming process.

[0317] FIGS. 54(a), 54(b) and 54(c) are perspective views showing basemembers 185A, 185B and 185C, respectively. The base member 185A iscomposed of a joined member having two plate-shaped members 159A and159B joined with each other. The direction of polarization of theplate-shaped member 159A (shown by arrow 165) and the direction ofpolarization of the plate-shaped member 159B (shown by arrow 166) areexactly opposite to each other, and are perpendicular to one main faceand the other main face. A direction of the axis of polarization of theplate-shaped member 159A and a direction of the axis of polarization ofthe plate-shaped member 159B, respectively, are directed from thecentral plane 167 toward the main faces. Vibrators as shown in FIGS. 46,51, 52 and 53 can be manufactured by cutting this base member.

[0318] The base member 185B is composed of a joined member having twoplate-shaped members 169A and 169B joined with each other. A directionof polarization of the plate-shaped member 169A (shown by arrow 180) anda direction of polarization of the plate-shaped member 169B (shown byarrow 181) are exactly opposite to each other, and are perpendicular toone main face and the other main face. A direction of the axis ofpolarization of the plate-shaped members are directed from therespective main faces toward the central plane. A vibrator as shown inFIG. 49 can be manufactured by cutting this base member.

[0319] The base member 185C is composed of a joined member having twoplate-shaped members 186A and 186B joined with each other. A directionof polarization of the plate-shaped member 186A (shown by arrow 182) anda direction of polarization of the plate-shaped member 186B (shown byarrow 183) are exactly opposite to each other, and are inclined at aspecified slant angle to one main face and the other main face.

[0320] FIGS. 55 to 57 illustrate a vibrator and a vibratory gyroscopewhich are preferable in case that the axis of polarization of each ofthe plate-shaped members is oriented at a slant angle to the main facesas shown in FIG. 54(c). FIG. 55 is a perspective view showing a vibrator187 and its electrodes of a vibratory gyroscope of this embodiment, FIG.56 is a plan view showing a plane-normal vibration arm, and FIG. 57 is aplan view showing a plane-parallel vibration arm.

[0321] The vibrator 187 shown in FIG. 55 is provided with a fixing part157 fixed on an external fixing member, and three tuning-fork vibrationarms 188A, 189 and 188B. The whole vibrator is composed of a joinedmember having two plate-shaped members 186A and 186B joined with eachother.

[0322] One electrode 190A is formed on one main face of each of theplane-normal vibration arms 188A and 188B, and the other electrode 190Bis formed on the other main face. In the plane-parallel vibration arm189, three electrodes 191A, 191B and 191C are formed on one main face,and the opposite electrodes 191D, 191E and 191F are formed on the othermain face at positions, respectively, opposite to the electrodes 191A,191B and 191C. Gaps 160 are provided, respectively, between thevibration arms 188A and 189, and between the vibration arms 189 and188B.

[0323] For example, the middle plane-parallel vibration arm is driven asshown by arrow Q, and the vibration arms at both sides are resonated asshown by arrows P and R. In order to do so, for example, the electrodes191A, 191C and 191E of the plane-parallel vibration arm are grounded,and the electrodes 191B, 191D and 191F opposite to them are connected toan alternating-current power source 192. In this state, electric fieldsare generated from the electrode 191B toward the electrodes 191A and191C as shown by arrows 198 in one layered part 186A, and electricfields are generated from the electrodes 191D and 191F toward theelectrode 191E as shown by arrows 197 in the other layered part 186B.That is to say, it is necessary to make electric fields generated in onelayered part and electric fields generated in the other layered partreverse in direction to each other.

[0324] When the vibrator is turned around the Z axis as shown by ω inthis state, the vibration arms 188A and 188B, respectively, are vibratedin the Y-axis direction as shown by arrows S and U. At the same time,the middle vibration arm is vibrated in the Y-axis direction as shown byarrow T. According to the invention, electromotive forces are generatedamong the electrodes by vibration of the plane-normal vibration arm. Aturning angular rate is detected by measuring this voltage.

[0325] As shown in FIGS. 58 and 59, vibration arms 198A, 198B and 202can be also manufactured by joining plate-shaped members 200A and 200Bwith each other. In this example, directions 194 and 199 of polarizationof the plate-shaped members are inclined at a specified angle to themain faces, and the directions 194 and 199 are nearly equal to eachother in plane-parallel direction component but are opposite to eachother in plane-normal direction component. One electrode 190A is formedon one main face of each of the plane-normal vibration arms 198A and198B, and the other electrode 190B is formed on the other main face. Inthe plane-parallel vibration arm 202, as shown in FIG. 59, threeelectrodes 191A, 191B and 191C are formed on one main face, and theopposite electrodes 191D, 191E and 191F are formed on the other mainface at positions, respectively, opposite to the electrodes 191A, 191Band 191C.

[0326] For example, the middle plane-parallel vibration arm 202 isdriven as shown by arrow Q, and the vibration arms 198A and 198B at bothsides are resonated as shown by arrows P and R. In order to do so, forexample, the electrodes 191A, 191C, 191D and 191F of the plane-parallelvibration arm are grounded, and the electrodes 191B and 191E areconnected to an alternating-current power source 192. In this state, forexample, electric fields are generated from the electrodes 191A and 191Ctoward the electrode 191B as shown by arrows 201 in one layered part200A, and electric fields are generated from the electrodes 191D and191F toward the electrode 191E as shown by arrows 197 in the otherlayered part 200B. That is to say, the electric fields generated in onelayered part and the electric fields generated in the other layered partare made reverse in direction to each other. In the same way after this,a turning angular rate is detected.

[0327] Concrete experiment results are described in the following. Theabove-mentioned vibratory gyroscopes as shown in FIGS. 46 to 48 weremade. A Z plate of quartz crystal was used as each plate-shaped member.A two-layered electrode of Cr and Au was used as a material for anelectrode. An alternating electric field of 1 volt and 7.5 Hz infrequency was applied between the electrodes 163A and 163B, and avibrator was turned, and then a relation between a turning angular rateand an output voltage from the electrodes 155A, 155B, 155C and 155D wasmeasured. The result is shown in Table 1. A good linearity was foundbetween an output voltage and a turning angular rate. TABLE 1 Turningangular rate: (°/sec) −40 −30 −20 −10 0 Output voltage: (mV) −5.01 −3.76−2.52 −1.30 0.10 Turning angular rate: (°/sec) 10 20 30 40 Outputvoltage: (mV) 1.26 2.51 3.74 5

[0328] A sixth embodiment of the invention is described in thefollowing.

[0329]FIG. 60 shows a construction of an example of a vibrator of avibratory gyroscope of the invention, 60(a) is a side view, 60(b) is afront view, and 60(c) is a plan view. This example shows a vibratorygyroscope of a vertical-arrangement type in which a drive vibration anda detection vibration are vertical. In an example shown in FIGS. 60(a)to 60(c), a tuning-fork vibrator 205 forming the vibratory gyroscope iscomposed of three arms 206, 207 and 208 arranged nearly in parallel withone another, and a base part 209 joining these three arms. Among thethree arms the arms 206 and 208 at both sides form detection arms, andthe middle arm 207 forms a drive arm. As a material for the tuning-forkvibrator, it is preferable to use a piezoelectric material such aspiezoceramic, quartz crystal, a single crystal of LiTaO₃, LiNbO₃ or thelike, and particularly more preferable to use a single crystal ofquartz, LiTaO₃, LiNbO₃ or the like.

[0330] The tuning-fork vibrator 205 operates in the same way as avibrator known up to now. That is to say, the drive arm 207 is firstvibrated in the X-Z plane by means of an unillustrated driving meansprovided on the drive arm. And the left and right detection arms 206 and208 are resonated in the same X-Y plane. When the vibrator is turnedaround the axis of symmetry Z of the tuning fork at a turning angularrate ω in this state, a Coriolis force f acts on each of the detectionarms. Since the detection arms are vibrating in the X-Z plane, vibrationin the Y-Z plane is excited in the detection arms. A turning angularrate is measured by detecting this vibration by means of anunillustrated detecting means provided on each of the detection arms.

[0331] An important point in this invention is to fix a domain wheremovement of the vibrator is the least by supporting the tuning-forkvibrator at the small domain where there is locally a domain having theleast detection vibration in case of supporting the above-mentionedtuning-fork vibrator to form a vibratory gyroscope. Thanks to this, adetection vibration can be effectively generated by a Coriolis forcewithout damping, the Q value of the detection vibration can be madehigher, and the sensitivity can be improved. Since the detectionvibration generated by a Coriolis force is small in amplitude, thisinvention is particularly effective to improve the sensitivity.Concretely, in the example shown in FIGS. 60(a) to 60(c), the vibratoris supported at a domain 210 nearly in the middle part of the base part209.

[0332] A method for supporting the vibrator is not limited inparticular, and any method known up to now as a method for adhering apiezoelectric member may be used. As an example, as shown in FIGS. 61(a)and 61(b), a specified hole 213 is provided at the nearly middle domain210 of the base part 209 in the direction of thickness, and the vibratorcan be fixed on a base part 211 of the vibratory gyroscope by insertingan end part 214 projecting from an arm 212 and perpendicularly to thelongitudinal direction of the arm 212 projecting from the base part 211into the hole 213. Fixing the end part 214 and the hole 213 onto eachother can be performed by applying metallization to the surface of theend part and/or the internal surface of the hole and then soldering orbrazing, or by providing resin between the end part and the hole.Although the base part 209 is supported on one surface of it in theexample shown in FIGS. 61(a) and 61(b), the base part can be alsosupported on both surfaces of it. And it is possible also to provide athrough hole instead of the hole 213, pass a supporting arm through thethrough hole, and fix both end parts of the supporting arm onto the basepart 211 of the vibratory gyroscope.

[0333] In the above-mentioned example, the reason why the nearly middlepart 210 of the main face of the base part 209 is assumed to be a smalldomain where there is locally a domain having the smallest detectionvibration is as follows. The inventors first applied a natural modeanalysis by means of a finite element analysis method to a vibrator 205having the above-mentioned shape in order to examine whether or notthere is a small domain where there is locally a domain having thesmallest detection vibration in relation to the vibrator 205. And thevibration amplitudes at each domain of the tuning-fork vibrator in theX-Z plane (where a drive vibration is generated) and in the Y-Z plane(where a detection vibration is generated by a Coriolis force) in caseof assuming that the vibrator has been cut along the X-Z plane have beenobtained as distribution of the ratio of the vibration amplitude at eachdomain to the vibration amplitude at the maximum vibration amplitudepoint. FIG. 62 shows the result in the X-Z plane where a drive vibrationis generated, and FIG. 63 shows the result in the Y-Z plane where adetection vibration is generated by a Coriolis force.

[0334] In the example shown in FIGS. 62 and 63, the respective domainsdiffer in color from orange, yellow, light-green, light blue, dark-blueand purple to show domains each of whose colors represents the ratio ofthe vibration amplitude at a domain to the vibration amplitude at themaximum vibration amplitude point, and in this invention, an orange partis a small domain where there is locally a domain having the smallestvibration whose amplitude is less than one thousandth of the amplitudeat the maximum vibration amplitude point. In this example, FIG. 62 showsthe ratio in comparison with the maximum vibration amplitude point in adrive vibration (plane-parallel vibration), and FIG. 63 shows the ratioin comparison with the maximum vibration amplitude point in thedetection vibration (plane-normal vibration), and from the result shownin FIG. 63, it has been confirmed that there is a small domain wherethere is locally a domain having the smallest detection vibration. Andsimilarly to the example shown in FIG. 60, it has been founded thatsupporting the vibrator at the nearly middle domain 210 of the mainfaces at both sides of the base part 209 results in not only supportingthe vibrator at a small domain where there is locally a domain havingthe smallest detection vibration known from FIG. 63 but also supportingthe vibrator at a small domain where there is locally a domain havingthe smallest drive vibration known from FIG. 62, and therefore in thisexample, supporting the vibrator in this way results in supporting thetuning-fork vibrator at a domain where a small domain where there islocally a domain having the smallest detection vibration and a smalldomain where there is locally a domain having the smallest drivevibration coincide with each other.

[0335] Taking the above-mentioned result into account, a result shown inTable 2 can be obtained by measuring the Q value of a drive vibration inthe X-Z plane, the Q value of a detection vibration in the Y-Z plane,and the sensitivity in relation to the example explained as a formerexample in FIG. 2 where the base part is fixed, the example where oneaxis is fixed, and the example where the vibrator is fixed as shown inFIG. 60 as the invention. From the result shown in Table 2, it has beenfound that both of the Q value of a drive vibration in the X-Z plane andthe Q value of a detection vibration in the Y-Z plane are higher and thesensitivity also is higher in the examples of the invention incomparison with the former examples. TABLE 2 Q of drive Q of detectionSensitivity vibration vibration (at 1 degree/sec) Base part fixed  4000 3000  1.1 mV One axis fixed  7000  8000  3.4 mV This embodiment 3000030000 10.8 mV

[0336] Although the above-mentioned example shows an example of usingthree arms as a tuning-fork vibrator, it is a matter of course that thenumber of arms is not limited to three and the invention can be alsoapplied to another number of arms such as four arms, five arms, or thelike. Although the above-mentioned example shows an example ofgenerating a drive vibration in the X-Z plane and a detection vibrationin the Y-Z plane in FIG. 60, it is a matter of course that the inventioncan be also applied to a gyroscope in which the shape of a vibrator 1 iskept as it is and a relation between both vibrations is reverse, namely,a drive vibration is generated in the Y-Z plane and a detectionvibration is generated in the X-Z plane.

[0337] Although the above-mentioned example explains an example of avibratory gyroscope of a vertical-arrangement type in which a drive modevibration and a detection mode vibration are vertical, the invention canbe preferably applied to a vibratory gyroscope of ahorizontal-arrangement type in which a drive mode vibration and adetection mode vibration are horizontal in the same plane. An example inwhich a finite element analysis was applied to a vibratory gyroscope ofa horizontal-arrangement type in the same way as the above-mentionedexample is described in the following.

[0338]FIG. 64 shows an example of the result of applying a natural modeanalysis by means of a finite element analysis method to a detectionmode vibration in a vibrator composed of a T-shaped arm and a base part.Since this vibrator was described in FIGS. 3 to 5, the description atthat time is quoted. In FIG. 64 also, vibrations in the respectivedomains are classified by color according to the ratio of the amplitudeof vibration at each domain to that at the maximum vibration amplitudepoint in the same way as FIGS. 62 and 63. In the example shown in FIG.64 also, it has been confirmed that there is a small domain where thereis locally a domain having the smallest detection vibration in themiddle of the base part. Actually, a result shown in Table 3 can beobtained by measuring the Q value of a drive vibration, the Q value of adetection vibration in the same plane as the drive vibration, and thesensitivity in relation to the example explained in FIG. 2 where thebase part is fixed and the example where the vibrator shown in FIG. 64is supported at a small domain where there is locally a domain havingthe smallest detection vibration as the invention. From the result shownin Table 3, it has been found that the Q value of a drive vibration ismade slightly higher and the Q value of a detection vibration is madeextraordinarily higher and the sensitivity also is made higher in theexample of the invention in comparison with the former examples. TABLE 3Q of drive Q of detection Sensitivity vibration vibration (at 1degree/sec) Base part fixed 3000  200 0.1 mV Node fixed 5000 3000 1.1 mV(this embodiment)

[0339]FIG. 65 shows an example of the result of applying a natural modeanalysis by means of a finite element analysis method to a detectionmode vibration in a vibrator composed of a Y-shaped arm and a base part.Since this vibrator was described in FIGS. 24, 25 and 27, thedescription at that time is quoted. In FIG. 65 also, in the same way asthe example shown in FIG. 64, color classifications are used toillustrate that it has been confirmed that there is a small domaindepicted in orange where there is locally a domain having the smallestdetection vibration in the middle of the base part. By actuallymeasuring the Q value of a drive vibration, the Q value of a detectionvibration in the same plane as the drive vibration, and the sensitivityin relation to the example explained in FIG. 2 where the base part isfixed and the vibrator shown in FIG. 6, in the same way as the vibratorshown in FIG. 64, it has been found that the Q value of a drivevibration is made slightly higher and the Q value of a detectionvibration is made extraordinarily higher and furthermore the sensitivityalso is made higher in the example of the invention in comparison withthe former examples.

[0340] When a natural mode analysis by means of a finite elementanalysis method has been also applied to a drive mode vibration in avibrator having a T-shaped arm shown in FIG. 64 and a vibrator having aY-shaped arm shown in FIG. 65, it has been found that the small domainwhere there is locally a domain having the smallest detection modevibration and the small domain where there is locally a domain havingthe smallest drive mode vibration do not coincide with each other.

[0341]FIGS. 66 and 67 use color to depict the result of applying anatural mode analysis by means of a finite element analysis method to avibrator having the opposite Y-shaped arms joined with the joint of twobase parts. Since this vibrator was described in FIGS. 28 and 29, thedescription at that time is quoted. An example shown in FIG. 66 is aresult in relation to a drive mode vibration, and an example shown inFIG. 67 is a result in relation to a detection mode vibration. From theexample shown in FIG. 66, color is used to depict variations in theratio of amplitude at a domain to amplitude at the maximum vibrationamplitude point; and in the same way as the examples shown in FIGS. 64and 65, it has been confirmed that there is a small domain where thereis locally a domain having the smallest detection vibration at therespective middle points of both base parts and an intersecting point ofthe opposite Y-shaped arms and the joint of the two base parts. From theexample shown in FIG. 67, color is used to illustrate that it has beenconfirmed that there is a small domain depicted in orange where there islocally a domain having the smallest drive vibration also in a drivemode vibration. In the example shown in FIG. 66, it has been foundedthat supporting the vibrator at the respective middle points of bothbase parts and an intersecting point of the opposite Y-shaped arms andthe joint of the two base parts results in also supporting the vibrateor at the small domain where there is locally a domain having thesmallest drive mode vibration as known from FIG. 67, and therefore inthis example, it results in supporting the vibrator at the domain wherethe small domain where there is locally a domain having the smallestdetection vibration and the small domain where there is locally a domainhaving the smallest drive vibration coincide with each other.

[0342] When the Q value of a drive vibration, the Q value of a detectionvibration in the same plane as the drive vibration, and the sensitivityhave been actually measured in relation to the example explained in FIG.2 where the base part is fixed and the example where the vibrator issupported at the small domains at each of which there is locally adomain having the smallest detection vibration like the invention,namely, at the respective middle points of both base parts and anintersecting point of the opposite Y-shaped arms and the joint of thetwo base parts, the results shown in Tables 4 and 5 have been able to beobtained. Hereupon, the result of Table 3 shows an example of supportingthe vibrator at the intersecting point of the opposite Y-shaped arms andthe joint of the two base parts, and the result of Table 4 shows anexample of supporting the vibrator at the respective two middle pointsof both base parts. From the results shown in Tables 4 and 5, it hasbeen found that the Q value of a drive vibration is made slightly higherand the Q value of a detection vibration is made extraordinarily higher,and furthermore the sensitivity is made higher in any of the examples ofthe invention in comparison with the former examples. TABLE 4 Q of driveQ of detection Sensitivity vibration vibration (at 1 degree/sec) Basepart fixed 4000  300 0.2 mV Node fixed 5000 3000 1.3 mV (thisembodiment)

[0343] TABLE 5 Q of drive Q of detection Sensitivity vibration vibration(at 1 degree/sec) Base part fixed 4000  300 0.2 mV Node fixed 5000 40001.5 mV (this embodiment)

[0344] Comparing Table 2 showing the result of a vibratory gyroscope ofa vertical-arrangement type and Tables 3 to 5 each of which shows theresult of a vibratory gyroscope of a horizontal-arrangement type witheach other among the examples of the invention, it has been found thatin any example of the invention the Q value of a detection modevibration is made one digit or so higher and the invention is moreeffective to a vibratory gyroscope of a horizontal-arrangement typehaving naturally a small Q value of the detection mode vibration.

[0345] A seventh embodiment of the invention is described in thefollowing.

[0346]FIG. 68 shows a construction of an example of a vibratorygyroscope 255 using a piezoelectric member already proposed by theapplicants. In an example shown in FIG. 68, a vibratory gyroscope isprovided with a tuning-fork vibrator 234 formed by joining a pair ofvibration arms 232 a and 232 b with bending-vibration pieces in the X-Yplane, a base part 236 for fixing this tuning-fork vibrator on anexternal fixing member 235 in the X-Y plane, electrodes 237A, 237B, 237Cand 237D which are provided on the tuning-fork vibration pieces 232 aand 232 b and are used for driving the tuning-fork vibration pieces, andelectrodes 238A, 238B, 238C and 238D used for obtaining an angular speedfrom vibration of the base part 236.

[0347] In the vibratory gyroscope having the construction shown in FIG.68, the tuning-fork vibration pieces 232 a and 232 b are vibrated in theX-Y plane so as to be exactly reverse in phase to each other by means ofthe electrodes 237A to 237D in a turning system with the Z axis as thecentral axis. When a turning angular rateω acts around the Z axis inthis state, a Coriolis force makes forces F1 and F2 which are reverse inphase to each other act on the tuning-fork vibration pieces along the Yaxis. As the result, moments M1 and M2 in the same direction act on bothends of the bending-vibration pieces of the tuning-fork vibrator 234. Aturning angular rate ω can be measured by detecting deformation of thebase part caused by the moments M1 and M2 by means of the electrodes238A to 238D.

[0348] In the vibratory gyroscope 255 having the construction shown inFIG. 68 which acts in this way, for example, in case of using a singlecrystal of lithium tantalate (LiTaO₃) as a piezoelectric material andcutting it along the 130° Y crystal face, driving and detection areperformed as described in the following. As seen from a sectional viewof a part having the electrodes 237A to 237D of the tuning-forkvibration piece shown as an example in FIG. 69, the electrodes 237A to237D are formed on end parts of both main faces of each of thetuning-fork vibration pieces so that each two of the electrodes can forma pair. And in FIG. 69, it is possible to contract the right side ofeach tuning-fork vibration piece and extend the left side by applyingvoltages reverse in phase to each other, respectively, to a pair ofelectrodes 237A and 237B and a pair of electrodes 237C and 237D. Thus,it is possible to give a drive vibration from left to right to thevibration pieces 232 a and 232 b in FIG. 69 by applying alternatingvoltages reverse in phase to each other to the pair of electrodes 237Aand 237B and the pair of electrodes 237C and 237D. And a turning angularrate ω can be obtained by performing the above-mentioned operation inthe reverse manner.

[0349] A former vibratory gyroscope 255 having the above-mentionedconstruction can act with no problem in an ordinary angular speedmeasurement. In case of performing an angular speed detection of highaccuracy as demanded in recent years, however, as shown in FIG. 70, ineach of the tuning-fork vibration pieces and the base part an electricfield E1 is applied to each pair of the pair of electrodes 237A (238A)and 237B (238B) and the pair of electrodes 237C (238C) and 237D (238D),and additionally to this, there is a horizontal-leakage electric fieldE2, although it is very weak, and since unnecessary displacements aregenerated in the tuning-fork vibration pieces and the base part due tothis leakage electric field, there is a problem that this leakageelectric field causes noises. Therefore, it has been impossible toperform an angular speed detection of high accuracy.

[0350]FIG. 71 shows a construction of an example of a vibratorygyroscope using a piezoelectric member of the invention. In an exampleshown in FIG. 71, a vibratory gyroscope 215 is provided with atuning-fork 218 formed by joining a pair of tuning-fork vibration pieces216 a and 216 b with bending-vibration pieces 256 a and 256 b in the X-Yplane, a base part 220 for fixing this tuning-fork vibrator 218 on anexternal fixing member 219 in the X-Y plane, electrodes 221A, 221B, 221Cand 221D which are provided on the tuning-fork vibration pieces and areused for driving the tuning-fork vibration pieces, and electrodes 223A,223B, 223C and 223D used for obtaining an angular speed from vibrationof the base part 220. The tuning-fork vibration pieces, thebending-vibration pieces, the base part, and the fixing member whichform the vibratory gyroscope are formed out of a piezoelectric materialin one body, and concretely, are formed out of piezoceramic such as PZTor the like, or a piezoelectric single crystal of quartz, lithiumtantalate or the like.

[0351] The construction of the vibratory gyroscope 215 is the same asthat of the above-mentioned former vibratory gyroscope. An importantpoint in the vibratory gyroscope of the invention shown in FIG. 71 isthat through holes 222 a, 222 b and 224 passing through both main facesare provided, respectively, between a pair of electrodes 221A (223A) and221B (223B) and between a pair of electrodes 221C (223C) and 221D (223D)in the tuning-fork vibration pieces 216 a and 216 b and the base part220. Although the through holes 222 a, 222 b and 224 are not limited insize in particular, it is preferable to make each through hole equal toor longer than the longitudinal length of each electrode, provide eachthrough hole in a range of ⅓ to ⅔ of the arm length from the arm base,and form the piezoelectric member out of a 130° Y plate of lithiumtantalate (LiTaO₃).

[0352] The vibratory gyroscope of the invention shown in FIG. 71 alsoacts in the same way as the above-mentioned former example and vibratesthe tuning-fork vibration pieces in the X-Y plane exactly reverse inphase to each other by means of the electrodes 221A to 221D in a turningsystem with the Z axis as the central axis. When a turning angular rateω acts around the Z axis in this state, a Coriolis force makes forces F1and F2 which are reverse in phase to each other along the Y axis act onthe tuning-fork vibration pieces. As the result, moments M1 and M2 inthe same direction act on both ends of the bending-vibration pieces ofthe tuning-fork vibrator 218. A turning angular rate ω can be measuredby detecting deformation of the base part caused by the moments M1 andM2 by means of the electrodes 223A to 223D.

[0353] In an example of the invention, a sectional view of a part of thetuning-fork vibration piece 216 a having the through hole 222 a is shownin FIG. 72, and in case of making the tuning-fork vibration piece 216 adrive-vibrate by applying alternating voltages reverse in phase to eachother, respectively, to the pair of electrodes 221A and 221B and thepair of electrodes 221C and 221 D, since even when there is ahorizontal-leakage electric field directed from one pair of electrodesto the other pair of electrodes there is no piezoelectric member in thethrough hole 222 a, no unnecessary displacement is generated in thetuning-fork vibration piece. And since a vibratory gyroscope of theinvention comprising arms having through holes can reduce the arms inrigidity by forming the through holes in the arms, it can obtain a drivevibration and a detection vibration in high efficiency. As the result,the invention can perform a high-accuracy angular speed detection.

[0354]FIG. 73 shows a construction of another example of a vibratorygyroscope using a piezoelectric member of the invention. In an exampleshown in FIG. 73, the same symbols are given to the same members asthose of FIG. 71, and description of them is omitted. Differently fromthe example shown in FIG. 71, the example shown in FIG. 73 uses a quartzcrystal having the a axis of a triad axis of symmetry in a specifiedplane as a piezoelectric material. In the example shown in FIG. 73,therefore, as seen from a sectional view of a part of the tuning-forkvibration piece 216 a having the through hole 222 a as an example inFIG. 74, a pair of electrodes 221A and 221B and a pair of electrodes221C and 221D are formed, respectively, on the outside faces and theinside faces facing the through hole 222 a (222 b) of each of thetuning-fork vibration pieces. In this example also, since there is noquartz crystal as a piezoelectric material in the through hole 222 a(222 b), unnecessary displacement can be removed.

[0355] Although in the above-mentioned example a vibratory gyroscopecomprising a tuning-fork 218 formed by joining a pair of tuning-forkvibration pieces 216 a and 216 b with bending-vibration pieces 256 a and256 b in the X-Y plane, a base part 220 for fixing this tuning-forkvibrator 218 on an external fixing member 219 in the X-Y plane,electrodes 221A to 221D which are provided on the tuning-fork vibrationpieces and are used for driving the tuning-fork vibration pieces, andelectrodes 223A to 223D used for obtaining an angular speed fromvibration of the base part 220 has been described as an example, it is amatter of course that any vibratory gyroscope having another compositionusing an arm composed of a piezoelectric material as a vibrator canobtain an effect of the invention.

[0356] A vibrator 257 of FIG. 75 comprises a fixing part 260, in itscentral portion, having a tetragonal-shaped central part 260 a and fourextended parts 206 b protruding from the central part. A pair of mainarms 258P and 258Q extend from the fixing part 260. In each of the mainarms, each main part 3 extends from each extended part 260 b, and eachbending-vibration piece 259 extends perpendicular to the main part 3from the other end part 3 b. Both ends of each bending vibration piece259 are connected with the main parts 3. Consequently, each space 262 isformed and enclosed with the fixing part 260, a pair of the main parts 3and the bending-vibration piece 259. A pair of bending-vibration pieces261 are provided with and extended from the central part 260 a of thefixing part 260.

[0357] Each bending-vibration piece 259 of each main arm is bent andvibrated as shown by an arrow “U” by applying alternating voltage to thepredetermined vibrating means not shown in FIG. 75. When the vibrator257 is turned around the z-axis, each main part 3 is bent and vibratedaround the joint near one end 3 a. This bending vibration of the mainparts causes bending vibration as shown by arrows “V” to thebending-vibration pieces 261, from which detection signals may beobtained and thus a turning angular rate may be calculated.

[0358]FIG. 76 shows another embodiment of the present inventionincluding a fixing part 300 having a base part 301 extending therefromin a first direction. A bending vibration piece 303 is attached at thedistal end of base part 301, and extends in a direction substantiallyperpendicular to the direction in which the base part extends. A throughhole or hollow portion 307 is formed through the entire thickness of thebase part 301, and allows the length of the base part to be reduced whenthe vibrator is operating at the same frequency as that of a similarvibrator having no through hole or hollow portion in the base part.Consequently, the overall size of the vibrator can be reduced, as well.In addition, the through hole or hollow portion also removes unnecessarydisplacements in the vibrator, as explained earlier herein.

[0359] FIGS. 77(a) and 77(b) show that the through hole or hollowportion 307 formed through the base part 301 can take a variety ofshapes, such as a diamond shape or a hexagonal shape.

[0360]FIG. 78 shows another embodiment of the present invention similarto that shown in FIG. 76, but also including additional through holes orhollow portions 309 formed through opposite end portions of the bendingvibration piece 303.

[0361]FIG. 79 shows another embodiment of the present inventionincluding a fixing part 300 and opposed base parts 301 and 302 extendingfrom fixing part 300. At the distal end of each base part, bendingvibration pieces 303 and 304, respectively, extend in a directionsubstantially perpendicular to the extension direction of the respectivebase parts 301 and 302. Also extending from the fixing part 300 areopposed resonant arms 305 and 306, which are aligned substantially onthe center line of gravity passing through the vibrator.

[0362]FIG. 79 shows that through holes or hollow portions 307 and 308are formed through the entire thickness of the base parts 301 and 302.Use of the through holes or hollow portions 307 and 308 in the baseparts 301 and 302 allows the length of the base parts to be reduced whenthe vibrator is operating at the same frequency as that of a vibratorhaving no through holes or hollow portions in the base parts. As aresult, the overall size of the vibrator can be reduced, as well. Inaddition, the through holes or hollow portions also remove unnecessarydisplacements in the vibrator, as explained earlier herein.

[0363]FIG. 80 shows another embodiment of a vibrator in accordance withthe present invention, which is similar to the vibrator shown in FIG.79, except that through holes or hollow portions 309 are formed throughthe distal ends of each bending vibration piece 303 and 304. FIG. 80also shows that through holes or hollow portions 310 can also be formedthrough the thickness of the resonant arms 305 and 306.

[0364] As explained earlier herein, use of through holes or hollowportions in the bending vibration pieces and/or the resonant armsenhances the sensitivity of the vibrator and reduces unnecessarydisplacement. And, as explained in the context of FIG. 79, use of thethrough holes or hollow portions also allows the length of the bendingvibration pieces and the resonant arms to be reduced, resulting in sizereduction in the overall vibrator, as well.

[0365]FIG. 81 is an enlarged view of circled region A from FIG. 80, andshows that the through hole or hollow portion 309 passing through thevibrator essentially takes the shape of a truncated cone. That is, thelateral width of the through hole or hollow portion 309 increases as thethrough hole extends away from its respective base part. In the contextof the resonant arms 305 and 306, the lateral width of the through holeor hollow portion 310 also increases as the through hole or hollowportion extends away from the fixing part 300. By shaping the throughhole or hollow portion in this fashion, the stress distributionthroughout the part becomes more uniform, and thus further enhancesvibrator sensitivity.

[0366]FIG. 81 also shows that the electrodes 311 and 312 are positionedon the upper and side surfaces of the respective part. Forming theelectrode 311 as shown in FIG. 81 allows application of the electricfield along the polarized axis of the underlying crystal (e.g., quartz).

[0367]FIG. 82 shows another embodiment of the vibrator of the presentinvention, which is similar to that shown in FIG. 80, but also includesweight members 320 at the distal end portions of the bending vibrationpieces and the resonant arms. These weight members allow the length ofthe bending vibration pieces (303, 304) and the resonant arms (305, 306)to be reduced when the vibrator is operating at the same frequency asthat of a similar vibrator without these weight members.

[0368]FIG. 83 shows another embodiment of the vibrator according to thepresent invention, which is similar to that shown in FIG. 82, but alsoincludes through holes or hollow portions 307 and 308 formed throughbase parts 301 and 302. The structure of FIG. 83 allows the length ofthe base parts 301 and 302 to be reduced when the vibrator is operatingat the same frequency as that of the vibrator shown in FIG. 82.Furthermore, since the weight of the vibrator shown in FIG. 83 isreduced as compared with the vibrator shown in FIG. 82, the vibratorshown in FIG. 83 is less sensitive to vibration disturbances contributedby external sources.

What is claimed:
 1. A vibratory gyroscope for detecting a turningangular rate about an axis of rotation, said vibratory gyroscopecomprising: a vibrator comprising (i) a fixing part arranged in a plane,(ii) a substantially straight base part arranged in said plane andhaving a first end attached to said fixing part and a second end opposedthereto in the longitudinal direction of said base part, (iii) at leastone bending vibration piece arranged in said plane and having a firstend attached to a portion of said base part other than said first end ofsaid base part, and a second end distal from said first end in alongitudinal direction of said bending vibration piece, the longitudinaldirection of said bending vibration piece intersecting the longitudinaldirection of said base part, and (iv) at least one pair of resonant armsarranged within said plane and extending from said fixing part, whereinsaid base part and said bending vibration piece both vibrate in abending vibration mode substantially within said plane using said firstends thereof, respectively, as their fulcrum, wherein said resonant armsresonate with vibration of said base part, and wherein one of a throughhole and a hollow portion is formed through at least one of said basepart, said bending vibration piece, and said resonant arms, said throughhole and/or said hollow portion having a lateral width that increases assaid through hole and/or said hollow portion extends along the length ofsaid at least one of said base part, said bending vibration piece andsaid resonant arms; excitation means for exciting vibration of one ofsaid base part and said bending vibration piece in said plane; anddetection means for detecting bending vibration of said vibratorgenerated by Coriolis force within said vibrator as a result of saidvibrator being rotated around said axis of rotation; wherein one of saidexcitation means and said detection means is positioned on said bendingvibration piece.
 2. The vibratory gyroscope according to claim 1,wherein said through hole and/or said hollow portion is formed throughsaid base part, and said lateral width thereof increases as said throughhole and/or said hollow portion extends toward said second end of saidbase part.
 3. The vibratory gyroscope according to claim 1, wherein saidthrough hole and/or said hollow portion is formed through said bendingvibration piece, and said lateral width thereof increases as saidthrough hole and/or said hollow portion extends toward said second endof said bending vibration piece.
 4. A vibratory gyroscope according toclaim 1, wherein said through hole and/or said hollow portion is formedthrough said resonant arms, and said lateral width thereof increases assaid through hole and/or said hollow portion extends away from saidfixing part.
 5. A vibrator comprising: a fixing part arranged in aplane; a substantially straight base part arranged in said plane andhaving a first end attached to said fixing part and a second end opposedthereto in the longitudinal direction of said base part; at least onebending vibration piece arranged in said plane and having a first endattached to a portion of said base part other than said first end ofsaid base part, and a second end distal from said first end in alongitudinal direction of said bending vibration piece, the longitudinaldirection of said bending vibration piece intersecting the longitudinaldirection of said base part; at least one pair of resonant arms arrangedwithin said plane and extending from said fixing part, wherein said basepart and said bending vibration piece both vibrate in a bendingvibration mode substantially within said plane using said first endsthereof, respectively, as their fulcrum, wherein said resonant armsresonate with vibration of said base part, and wherein one of a throughhole and a hollow portion is formed through at least one of said basepart, said bending vibration piece, and said resonant arms, said throughhole and/or said hollow portion having a lateral width that increases atsaid through hole and/or said hollow portion extends along the length ofsaid at least one of said base part, said bending vibration piece andsaid resonant arms; and excitation means for exciting vibration of oneof said base part and said bending vibration piece in said plane.
 6. Thevibrator according to claim 5, wherein said through hole and/or saidhollow portion is formed through said base part, and said lateral widththereof increases as said through hole and/or said hollow portionextends toward said second end of said base part.
 7. The vibratoraccording to claim 5, wherein said through hole and/or said hollowportion is formed through said bending vibration piece, and said lateralwidth thereof increases as said through hole and/or said hollow portionextends toward said second end of said bending vibration piece.
 8. Avibrator according to claim 5, wherein said through hole and/or saidhollow portion is formed through said resonant arms, and said lateralwidth thereof increases as said through hole and/or said hollow portionextends away from said fixing part.
 9. A vibratory gyroscope fordetecting a turning angular rate about an axis of rotation, saidvibratory gyroscope comprising: a vibrator comprising (i) a fixing partarranged in a plane, (ii) a substantially straight base part arranged insaid plane and having a first end attached to said fixing part and asecond end opposed thereto in the longitudinal direction of said basepart, (iii) at least one bending vibration piece arranged in said planeand having a first end attached to a portion of said base part otherthan said first end of said base part, and a second end distal from saidfirst end in a longitudinal direction of said bending vibration piece,the longitudinal direction of said bending vibration piece intersectingthe longitudinal direction of said base part, and (iv) at least one pairof resonant arms arranged within said plane and extending from saidfixing part, wherein said base part and said bending vibration pieceboth vibrate in a bending vibration mode substantially within said planeusing said first ends thereof, respectively, as their fulcrum, whereinsaid resonant arms resonate with vibration of said base part, andwherein one of a through hole and a hollow portion is formed throughsaid base part; excitation means for exciting vibration of one of saidbase part and said bending vibration piece in said plane; and detectionmeans for detecting bending vibration of said vibrator generated byCoriolis force within said vibrator as a result of said vibrator beingrotated around said axis of rotation; wherein one of said excitationmeans and said detection means is positioned on said bending vibrationpiece.
 10. A vibrator comprising: a fixing part arranged in a plane; asubstantially straight base part arranged in said plane and having afirst end attached to said fixing part and a second end opposed theretoin the longitudinal direction of said base part; at least one bendingvibration piece arranged in said plane and having a first end attachedto a portion of said base part other than said first end of said basepart, and a second end distal from said first end in a longitudinaldirection of said bending vibration piece, the longitudinal direction ofsaid bending vibration piece intersecting the longitudinal direction ofsaid base part; at least one pair of resonant arms arranged within saidplane and extending from said fixing part, wherein said base part andsaid bending vibration piece both vibrate in a bending vibration modesubstantially within said plane using said first ends thereof,respectively, as their fulcrum, wherein said resonant arms resonate withvibration of said base part, and wherein one of a through hole and ahollow portion is formed through said base part; and excitation meansfor exciting vibration of one of said base part and said bendingvibration piece in said plane.
 11. A vibratory gyroscope for detecting aturning angular rate about an axis of rotation, said vibratory gyroscopecomprising: a vibrator comprising (i) a fixing part arranged in a plane,(ii) a substantially straight base part arranged in said plane andhaving a first end attached to said fixing part and a second end opposedthereto in the longitudinal direction of said base part, and (iii) atleast one bending vibration piece arranged in said plane and having afirst end attached to a portion of said base part other than said firstend of said base part, and a second end distal from said first end in alongitudinal direction of said bending vibration piece, the longitudinaldirection of said bending vibration piece intersecting the longitudinaldirection of said base part, wherein said base part and said bendingvibration piece both vibrate in a bending vibration mode substantiallywithin said plane using said first ends thereof, respectively, as theirfulcrum, and wherein one of a through hole and a hollow portion isformed through at least one of said base part and said bending vibrationpiece; excitation means for exciting vibration of one of said base partand said bending vibration piece in said plane; and detection means fordetecting bending vibration of said vibrator generated by Coriolis forcewithin said vibrator as a result of said vibrator being rotated aroundsaid axis of rotation; wherein one of said excitation means and saiddetection means is positioned on said bending vibration piece.
 12. Thevibratory gyroscope according to claim 11, wherein said through holeand/or said hollow portion has a lateral width that increases as saidthrough hole and/or said hollow portion extends along the length of saidat least one of said base part and said bending vibration piece.
 13. Thevibratory gyroscope according to claim 11, wherein said through holeand/or said hollow portion has a shape selected from the groupconsisting of rectangular, triangular, diamond and hexagonal.
 14. Thevibratory gyroscope according to claim 11, wherein said through holeand/or said hollow portion is formed through said base part, and alateral width thereof increases as said through hole and/or said hollowportion extends toward said second end of said base part.
 15. Thevibratory gyroscope according to claim 11, wherein said through holeand/or said hollow portion is formed through said bending vibrationpiece, and a lateral width thereof increases as said through hole and/orsaid hollow portion extends toward said second end of said bendingvibration piece.
 16. A vibrator comprising: a fixing part arranged in aplane; a substantially straight base part arranged in said plane andhaving a first end attached to said fixing part and a second end opposedthereto in the longitudinal direction of said base part; at least onebending vibration piece arranged in said plane and having a first endattached to a portion of said base part other than said first end ofsaid base part, and a second end distal from said first end in alongitudinal direction of said bending vibration piece, the longitudinaldirection of said bending vibration piece intersecting the longitudinaldirection of said base part; wherein said base part and said bendingvibration piece both vibrate in a bending vibration mode substantiallywithin said plane using said first ends thereof, respectively, as theirfulcrum, and wherein one of a through hole and a hollow portion isformed through at least one of said base part and said bending vibrationpiece; and excitation means for exciting vibration of one of said basepart and said bending vibration piece in said plane.
 17. The vibratoraccording to claim 16, wherein said through hole and/or said hollowportion has a lateral width that increases as said through hole and/orsaid hollow portion extends along the length of said at least one ofsaid base part and said bending vibration piece.
 18. The vibratoraccording to claim 16, wherein said through hole and/or said hollowportion has a shape selected from the group consisting of rectangular,triangular, diamond and hexagonal.
 19. The vibrator according to claim16, wherein said through hole and/or said hollow portion is formedthrough said base part, and a lateral width thereof increases as saidthrough hole and/or said hollow portion extends toward said second endof said base part.
 20. The vibrator according to claim 16, wherein saidthrough hole and/or said hollow portion is formed through said bendingvibration piece, and a lateral width thereof increases as said throughhole and/or said hollow portion extends toward said second end of saidbending vibration piece.
 21. A vibratory gyroscope for detecting aturning angular rate about an axis of rotation, said vibratory gyroscopecomprising: a vibrator comprising (i) a fixing part arranged in a plane,(ii) a substantially straight base part arranged in said plane andhaving a first end attached to said fixing part and a second end opposedthereto in the longitudinal direction of said base part, and (iii) atleast one bending vibration piece arranged in said plane and having afirst end attached to a portion of said base part other than said firstend of said base part, and a second end distal from said first end in alongitudinal direction of said bending vibration piece, the longitudinaldirection of said bending vibration piece intersecting the longitudinaldirection of said base part, wherein said base part and said bendingvibration piece both vibrate in a bending vibration mode substantiallywithin said plane using said first ends thereof, respectively, as theirfulcrum, and wherein one of a through hole and a hollow portion isformed through said base part; excitation means for exciting vibrationof one of said base part and said bending vibration piece in said plane;and detection means for detecting bending vibration of said vibratorgenerated by Coriolis force within said vibrator as a result of saidvibrator being rotated around said axis of rotation; wherein one of saidexcitation means and said detection means is positioned on said bendingvibration piece.
 22. The vibratory gyroscope according to claim 21,wherein said through hole and/or said hollow portion has a lateral widththat increases as said through hole and/or said hollow portion extendsalong the length of said base part.
 23. The vibratory gyroscopeaccording to claim 21, wherein said through hole and/or said hollowportion has a shape selected from the group consisting of rectangular,triangular, diamond and hexagonal.
 24. A vibrator comprising: a fixingpart arranged in a plane; a substantially straight base part arranged insaid plane and having a first end attached to said fixing part and asecond end opposed thereto in the longitudinal direction of said basepart; at least one bending vibration piece arranged in said plane andhaving a first end attached to a portion of said base part other thansaid first end of said base part, and a second end distal from saidfirst end in a longitudinal direction of said bending vibration piece,the longitudinal direction of said bending vibration piece intersectingthe longitudinal direction of said base part; wherein said base part andsaid bending vibration piece both vibrate in a bending vibration modesubstantially within said plane using said first ends thereof,respectively, as their fulcrum, and wherein one of a through hole and ahollow portion is formed through said base part; and excitation meansfor exciting vibration of one of said base part and said bendingvibration piece in said plane.
 25. The vibrator according to claim 24,wherein said through hole and/or said hollow portion has a lateral widththat increases as said through hole and/or said hollow portion extendsalong the length of said base part.
 26. The vibrator according to claim24, wherein said through hole and/or said hollow portion has a shapeselected from the group consisting of rectangular, triangular, diamondand hexagonal.